Intermediate Geometry : How to find the length of the side of a trapezoid

Study concepts, example questions & explanations for Intermediate Geometry

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Example Questions

Example Question #1 : How To Find The Length Of The Side Of A Trapezoid

Suppose the area of the trapezoid is \(\displaystyle 30\), with a height of \(\displaystyle 10\) and a base of \(\displaystyle 5\).  What must be the length of the other base?

 

Possible Answers:

\(\displaystyle 1\)

\(\displaystyle 15\)

\(\displaystyle 5\)

\(\displaystyle 2\)

\(\displaystyle 20\)

Correct answer:

\(\displaystyle 1\)

Explanation:

Write the formula for finding the area of a trapezoid.

\(\displaystyle A=\frac{h}{2}(b_1+b_2)\)

Substitute the givens and solve for either base.

\(\displaystyle 30=\frac{10}{2}(5+b_2)\)

\(\displaystyle 30=5(5+b_2)\)

\(\displaystyle 6=5+b_2\)

\(\displaystyle b_2=1\)

Example Question #1 : How To Find The Length Of The Side Of A Trapezoid

If the area of a trapezoid is \(\displaystyle 15\), the height of the trapezoid is \(\displaystyle 3\), and the base length is \(\displaystyle 8\), what must be the length of the other base?

 

Possible Answers:

\(\displaystyle 2\)

\(\displaystyle 6\)

\(\displaystyle 5\)

\(\displaystyle 1\)

\(\displaystyle 3\)

Correct answer:

\(\displaystyle 2\)

Explanation:

Write the formula for the area of a trapezoid.

\(\displaystyle A=\frac{h}{2}(b_1+b_2)\)

Substitute all the given values and solve for the base.

\(\displaystyle 15=\frac{3}{2}(8+b_2)\)

\(\displaystyle 10=8+b_2\)

\(\displaystyle b_2=2\)

Example Question #1 : How To Find The Length Of The Side Of A Trapezoid

An isosceles trapezoid has base measurements of \(\displaystyle 19\) and \(\displaystyle 6\). The perimeter of the trapezoid is \(\displaystyle 35\). Find the length for one of the two remaining sides. 

Possible Answers:

\(\displaystyle 7.5\)

\(\displaystyle 10\)

\(\displaystyle 12.5\)

\(\displaystyle 5\)

Correct answer:

\(\displaystyle 5\)

Explanation:

To solve this problem, first note that an isosceles trapezoid has two parallel bases that are nonequivalent in length. Additionally, an isosceles trapezoid must have two nonparallel sides that have equivalent lengths. Since this problem provides the length for both of the bases as well as the total perimeter, the missing sides can be found using the following formula: Perimeter= Base one \(\displaystyle +\) Base two \(\displaystyle +\) \(\displaystyle 2\)(leg), where the length of "leg" is one of the two equivalent nonparallel sides. 

Thus, the solution is:

\(\displaystyle 35=19+6+2(leg)\)

\(\displaystyle 35=25+2(leg)\)

\(\displaystyle 2(leg)=35-25\) 

\(\displaystyle 2(leg)=10\)
\(\displaystyle leg=\frac{10}{2}=5\)

Check the solution by plugging in the answer:

\(\displaystyle 35=19+6+2(5)\)

\(\displaystyle 35=25+10\)

\(\displaystyle 35=35\)


Example Question #1 : How To Find The Length Of The Side Of A Trapezoid

An isosceles trapezoid has base measurements of \(\displaystyle 11\) and \(\displaystyle 7\). Additionally, the isosceles trapezoid has a height of \(\displaystyle 4\). Find the length for one of the two missing sides. 

Possible Answers:

\(\displaystyle 2\sqrt{20}\)

\(\displaystyle \sqrt{20}\)

\(\displaystyle \sqrt{16}\)

\(\displaystyle 20\)

\(\displaystyle 2\sqrt{2}\)

Correct answer:

\(\displaystyle \sqrt{20}\)

Explanation:

In order to solve this problem, first note that an isosceles trapezoid has two parallel bases that are nonequivalent in length. Additionally, an isosceles trapezoid must have two nonparallel sides that have equivalent lengths. 

This problem provides the lengths for each of the bases as well as the height of the isosceles trapezoid. In order to find the length for one of the two equivalent nonparallel legs of the trapezoid, first use the height of the trapezoid to form right triangles on the interior of the trapezoid that each have a base length of \(\displaystyle 2\). See image below:

 Isos. trap intermediate geo
Note: the base length of \(\displaystyle 2\) can be found by subtracting the lengths of the two bases, then dividing that difference in half: 

\(\displaystyle 11-7=4\)

\(\displaystyle 4\div2=2\)

Now, apply the formula \(\displaystyle a^2+b^2=c^2\), where \(\displaystyle c=\) the length for one of the two equivalent nonparallel legs of the trapezoid. 

Thus, the solution is:

\(\displaystyle 2^2+4^2=c^2\)

\(\displaystyle 4+16=c^2\)

\(\displaystyle 20=c^2\)

\(\displaystyle c=\sqrt{20}\)

Example Question #5 : How To Find The Length Of The Side Of A Trapezoid

Isos. trap intermediate geo

The isosceles trapezoid shown above has base measurements of \(\displaystyle 12\) and \(\displaystyle 18\). Additionally, the trapezoid has a height of \(\displaystyle 15\). Find the length of side \(\displaystyle x\)

Possible Answers:

\(\displaystyle \sqrt{26}\)

\(\displaystyle 3\sqrt{15}\)

\(\displaystyle \sqrt{15}\)

\(\displaystyle 9\sqrt{26}\)

\(\displaystyle 3\sqrt{26}\)

Correct answer:

\(\displaystyle 3\sqrt{26}\)

Explanation:

In this problem the lengths for each of the bases and the height of the isosceles trapezoid is provided in the question prompt. In order to find the length for one of the two equivalent nonparallel legs of the trapezoid (side \(\displaystyle x\)), first use the height of the trapezoid to form right triangles on the interior of the trapezoid that each have a base length of \(\displaystyle 3\).

The base of the interior triangles is equal to \(\displaystyle 3\) because the difference between the two bases is equal to \(\displaystyle 6\). And, this difference must be divided evenly in half because the isosceles trapezoid is symmetric--due to the two equivalent nonparallel sides and the two nonequivalent parallel bases.  

Now, apply the pythagorean theorem: \(\displaystyle a^2+b^2=c^2\), where \(\displaystyle c=x\).

\(\displaystyle 3^2+15^2=c^2\)

\(\displaystyle 9+225=c^2\)

\(\displaystyle c^2=234\)

\(\displaystyle c=\sqrt{234}=\sqrt{9\times 26}=\sqrt{9}\sqrt{26}=3\sqrt{26}\)

Thus, \(\displaystyle x=3\sqrt{26}\)

Example Question #1 : How To Find The Length Of The Side Of A Trapezoid

Isos. trap intermediate geo

Using the isosceles trapezoid shown above, find the length for one of the two nonparallel equivalent sides. 

Possible Answers:

\(\displaystyle 14\)

\(\displaystyle 9\)

\(\displaystyle 5\)

\(\displaystyle 7\)

\(\displaystyle 16\)

Correct answer:

\(\displaystyle 7\)

Explanation:

To solve this problem, first note that an isosceles trapezoid has two parallel bases that are nonequivalent in length. Additionally, an isosceles trapezoid must have two nonparallel sides that have equivalent lengths. Since this problem provides the length for both of the bases as well as the total perimeter, the missing sides can be found using the following formula: Perimeter= Base one \(\displaystyle +\) Base two \(\displaystyle +\) \(\displaystyle 2\)(leg), where the length of "leg" is one of the two equivalent nonparallel sides. 

Thus, the solution is:

\(\displaystyle 39=17+8+2(leg)\)

\(\displaystyle 39=25+2(leg)\)

\(\displaystyle 2(leg)=39-25\)

\(\displaystyle 2(leg)=14\)

\(\displaystyle leg=\frac{14}{2}=7\)

Example Question #1 : How To Find The Length Of The Side Of A Trapezoid

An isosceles trapezoid has one base measurement of \(\displaystyle 45\) and the length for one of the nonparallel sides is \(\displaystyle 24\). The perimeter of the trapezoid is \(\displaystyle 119\). Find the length for the other base of the trapezoid.

Possible Answers:

Not enough information is provided in this problem. 

\(\displaystyle 93\)

\(\displaystyle 26\)

\(\displaystyle 24\)

\(\displaystyle 48\)

Correct answer:

\(\displaystyle 26\)

Explanation:

To solve this problem, first note that an isosceles trapezoid has two parallel bases that are nonequivalent in length. Additionally, an isosceles trapezoid must have two nonparallel sides that have equivalent lengths. 

Therefore, use the given information to apply the formula: 

Perimeter= Base one \(\displaystyle +\) Base two \(\displaystyle +\) \(\displaystyle 2\)(leg), where the length of "leg" is one of the two equivalent nonparallel sides.

Thus, the solution is:

\(\displaystyle 119=45+2(24) +Base\)

\(\displaystyle 119=48+45+Base\)

\(\displaystyle 119=93+Base\)

\(\displaystyle Base=119-93=26\) 

Example Question #1 : How To Find The Length Of The Side Of A Trapezoid

An isosceles trapezoid has base measurements of \(\displaystyle 13\) and \(\displaystyle 15\), respectively. Additionally, the isosceles trapezoid has a height that is \(\displaystyle \frac{1}{3}\) the measurement of the larger base. Find the length for one of the two equivalent nonparallel sides. 

Possible Answers:

\(\displaystyle 2\sqrt{13}\)

\(\displaystyle 2\sqrt{6}\)

\(\displaystyle \sqrt{26}\)

\(\displaystyle \sqrt{6}\)

\(\displaystyle 5\)

Correct answer:

\(\displaystyle \sqrt{26}\)

Explanation:

In order to solve this problem, first note that an isosceles trapezoid has two parallel bases that are nonequivalent in length. Additionally, an isosceles trapezoid must have two nonparallel sides that have equivalent lengths. 

This problem provides the lengths for each of the bases as well as informataion regarding the height of the isosceles trapezoid. In order to find the length for one of the two equivalent nonparallel legs of the trapezoid, use the height of the trapezoid to form right triangles on the interior of the trapezoid that each have a base length of \(\displaystyle 1\). The interior triangle base length of \(\displaystyle 1\) can be found by subtracting the lengths of the two bases, then dividing that difference in half: 

\(\displaystyle 15-13=2\)

\(\displaystyle \frac{2}{2}=1\)

In order to calculate the exact height of the isosceles trapezoid (as well as the interior triangle), find \(\displaystyle \frac{1}{3}\) of the larger base. Since the largest base of the trapezoid is \(\displaystyle 15\), the height of the trapezoid is: \(\displaystyle \frac{1}{3}\times15=\frac{15}{3}=5\)


Now you have enough information to apply the formula \(\displaystyle a^2+b^2=c^2\), where \(\displaystyle c=\) one of the missing sides. 

The final solution is:

\(\displaystyle 1^2+5^2=c^2\)

\(\displaystyle 1+25=c^2\)

\(\displaystyle c^2=26\)

\(\displaystyle c=\sqrt{26}\) 

Example Question #1 : How To Find The Length Of The Side Of A Trapezoid

An isosceles trapezoid has base measurements of \(\displaystyle 115\) and \(\displaystyle 163\). The perimeter of the trapezoid is \(\displaystyle 372\). Find the length for one of the two remaining sides. 

Possible Answers:

\(\displaystyle 45\)

\(\displaystyle 90\)

\(\displaystyle 48\)

\(\displaystyle 96\)

\(\displaystyle 47\)

Correct answer:

\(\displaystyle 47\)

Explanation:

To solve this problem, first note that an isosceles trapezoid has two parallel bases that are nonequivalent in length. Additionally, an isosceles trapezoid must have two nonparallel sides that have equivalent lengths. Since this problem provides the length for both of the bases as well as the total perimeter, the missing sides can be found using the following formula: Perimeter= Base one \(\displaystyle +\) Base two \(\displaystyle +\) \(\displaystyle 2\)(leg), where the length of "leg" is one of the two equivalent nonparallel sides. 

Thus, the solution is: 

\(\displaystyle 372=163+115+2(leg)\)

\(\displaystyle 372=278+2(leg)\)

\(\displaystyle 2(leg)=372-278=94\)

\(\displaystyle leg=\frac{94}{2}=47\)


Check the solution by plugging in the answer:

\(\displaystyle 372=163+115+2(47)\)
\(\displaystyle 372=372\)

Example Question #1 : How To Find The Length Of The Side Of A Trapezoid

An isosceles trapezoid has one base measurement of \(\displaystyle 100\) and the length for one of the nonparallel sides is \(\displaystyle 55\). The perimeter of the trapezoid is \(\displaystyle 301\). Find the length for the other base of the trapezoid.

Possible Answers:

\(\displaystyle 74\)

\(\displaystyle 81\)

\(\displaystyle 146\)

\(\displaystyle 73\)

\(\displaystyle 91\)

Correct answer:

\(\displaystyle 91\)

Explanation:

To solve this problem, first note that an isosceles trapezoid has two parallel bases that are nonequivalent in length. Additionally, an isosceles trapezoid must have two nonparallel sides that have equivalent lengths. 

Therefore, use the given information to apply the formula: 

Perimeter= Base one \(\displaystyle +\) Base two \(\displaystyle +\) \(\displaystyle 2\)(leg), where the length of "leg" is one of the two equivalent nonparallel sides.

Thus, the solution is:

\(\displaystyle 301=100+2(55) +Base\)

\(\displaystyle 301=100+110+Base\)

\(\displaystyle 301=210+Base\)

\(\displaystyle Base=301-210=91\) 

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