GED Math : Angles and Quadrilaterals

Study concepts, example questions & explanations for GED Math

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Example Questions

Example Question #91 : Squares, Rectangles, And Parallelograms

In Rhombus \displaystyle RHOM\displaystyle m \angle R = 60 ^{\circ }. If \displaystyle \overline{RO } is constructed, which of the following is true about \displaystyle \Delta RHO?

Possible Answers:

\displaystyle \Delta RHO is acute and isosceles, but not equilateral

\displaystyle \Delta RHO is obtuse and isosceles, but not equilateral

\displaystyle \Delta RHO is acute and equilateral

\displaystyle \Delta RHO is right and isosceles, but not equilateral

Correct answer:

\displaystyle \Delta RHO is obtuse and isosceles, but not equilateral

Explanation:

The figure referenced is below.

Rhombus

The sides of a rhombus are congruent by definition, so \displaystyle \overline{RH} \cong \overline{HO}, making \displaystyle \Delta RHO isosceles (and possibly equilateral).

Also, consecutive angles of a rhombus are supplementary, as they are with all parallelograms, so

\displaystyle m \angle H = 180^{\circ} - m \angle HRM = 180^{\circ} - 60 ^{\circ} = 120^{\circ}.

\displaystyle \angle H, having measure greater than \displaystyle 90^{\circ}, is obtuse, making \displaystyle \Delta RHO an obtuse triangle. Also, the triangle is not equilateral, since such a triangle must have three \displaystyle 60 ^{\circ} angles.

The correct response is that \displaystyle \Delta RHO is obtuse and isosceles, but not equilateral.

Example Question #92 : Squares, Rectangles, And Parallelograms

Given Quadrilateral \displaystyle ABCD, which of these statements would prove that it is a parallelogram?

I) \displaystyle \angle A \cong \angle B and \displaystyle \angle C \cong \angle D

II) \displaystyle \angle A \cong \angle C and \displaystyle \angle B \cong \angle D

III) \displaystyle \angle A and \displaystyle \angle B are supplementary and \displaystyle \angle C and \displaystyle \angle D are supplementary

Possible Answers:

Statement I only

Statement II only

Statement I, II, or III

Statement III only

Correct answer:

Statement II only

Explanation:

Statement I asserts that two pairs of consecutive angles are congruent. This does not prove that the figure is a parallelogram. For example, an isosceles trapezoid has two pairs of congruent base angles, which are consecutive. 

Statement II asserts that both pairs of opposite angles are congruent. By a theorem of geometry, this proves the quadrilateral to be a parallelogram.

Statement III asserts that two pairs of consecutive angles are supplementary. While all parallelograms have this characteristic, trapezoids do as well, so this does not prove the figure a parallelogram.

The correct response is Statement II only.

Example Question #3 : Angles And Quadrilaterals

You are given Parallelogram \displaystyle ABCD with \displaystyle AB = 12 , BC = 15. Which of the following statements, along with what you are given, would be enough to prove that Parallelogram \displaystyle ABCD is a rectangle?

I) \displaystyle m \angle A = 90 ^{\circ }

II) \displaystyle m \angle B = 90 ^{\circ }

III) \displaystyle m \angle C = 90 ^{\circ }

Possible Answers:

Statement II only

Statement I only

Statement I, II, or III

Statement III only

Correct answer:

Statement I, II, or III

Explanation:

A rectangle is defined as a parallelogram with four right, or \displaystyle 90 ^{\circ}, angles.

Since opposite angles of a paralellogram are congruent, if one angle measures \displaystyle 90 ^{\circ}, so does its opposite. Since consecutive angles of a paralellogram are supplementary - that is, their degree measures total \displaystyle 180 ^{\circ} - if one angle measures \displaystyle 90 ^{\circ}, then both of the neighboring angles measure \displaystyle 180 ^{\circ} - 90 ^{\circ} = 90 ^{\circ}.

In short, in a parallelogram, if one angle is right, all are right and the parallelogram is a rectangle. All three statements assert that one angle is right, so from any one, it follows that the figure is a rectangle. The correct response is Statements I, II, or III.

Note that the sidelengths are irrelevant.

Example Question #1 : Angles And Quadrilaterals

If the rectangle has a width of 5 and a length of 10, what is the area of the rectangle?

Possible Answers:

\displaystyle 50

\displaystyle 40

\displaystyle 75

\displaystyle 25

\displaystyle 100

Correct answer:

\displaystyle 50

Explanation:

Write the area for a rectangle.

\displaystyle A= LW

Substitute the given dimensions.

\displaystyle A = 10(5) = 50

The answer is:  \displaystyle 50

Example Question #3 : Angles And Quadrilaterals

In the figure below, find the measure of the largest angle.

3

Possible Answers:

\displaystyle 23^{\circ}

\displaystyle 151^{\circ}

\displaystyle 118^{\circ}

\displaystyle 128^{\circ}

Correct answer:

\displaystyle 151^{\circ}

Explanation:

Recall that in a quadrilateral, the interior angles must add up to \displaystyle 360^{\circ}.

Thus, we can solve for \displaystyle x:

\displaystyle x+9+(7x-10)+(3x-10)+(5x+3)=360

\displaystyle 16x-8=360

\displaystyle 16x=368

\displaystyle x=23

Now, to find the largest angle, plug in the value of \displaystyle x into each expression for each angle.

\displaystyle x+9=23+9=32

\displaystyle 7x-10=7(23)-10=151

\displaystyle 3x-10=3(23)-10=59

\displaystyle 5x+3=5(23)+3=118

The largest angle is \displaystyle 151^{\circ}.

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