ACT Math : Square of Sum

Study concepts, example questions & explanations for ACT Math

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Example Questions

Example Question #1 : How To Find The Square Of A Sum

Evaluate the following expression:

\(\displaystyle 2^{5}+(5*2)^{2}\)

Possible Answers:

\(\displaystyle 52\)

\(\displaystyle 61\)

\(\displaystyle 110\)

\(\displaystyle 132\)

\(\displaystyle 164\)

Correct answer:

\(\displaystyle 132\)

Explanation:

2 raised to the power of 5 is the same as multiplying 2 by itself 5 times so:

25 = 2x2x2x2x2 = 32

Then, 5x2 must first be multiplied before taking the exponent, yielding 102 = 100.

100 + 32 = 132

 

Example Question #2 : Squaring / Square Roots / Radicals

Expand:

\(\displaystyle (3x+5)^2\)

Possible Answers:

\(\displaystyle 9x^2-30x+25\)

\(\displaystyle 9x^2+25\)

\(\displaystyle 6x+10\)

\(\displaystyle 9x^2+30x+25\)

Correct answer:

\(\displaystyle 9x^2+30x+25\)

Explanation:

To multiply a difference squared, square the first term and add two times the multiplication of the two terms. Then add the second term squared.

\(\displaystyle (3x)^2+2(3x)(5)+(5)^2=9x^2+30x+25\)

Example Question #1 : How To Find The Square Of A Sum

Which of the following is the square of \(\displaystyle 4x + 7y\) ?

Possible Answers:

\(\displaystyle 16x^{2}+ 22xy+ 49y^{2}\)

\(\displaystyle 16x^{2}+ 28xy+ 49y^{2}\)

\(\displaystyle 16x^{2}+ 56xy+ 49y^{2}\)

\(\displaystyle 16x^{2} + 49y^{2}\)

\(\displaystyle 16x^{2}+ 11xy+ 49y^{2}\)

Correct answer:

\(\displaystyle 16x^{2}+ 56xy+ 49y^{2}\)

Explanation:

Use the square of a sum pattern, substituting \(\displaystyle 4x\) for \(\displaystyle A\) and \(\displaystyle 7y\) for \(\displaystyle B\) in the pattern:

\(\displaystyle (A+ B)^{2}= A^{2}+ 2AB + B^{2}\)

\(\displaystyle (4x + 7y)^{2}= (4x)^{2}+ 2 (4x) (7y) + (7y)^{2}\)

\(\displaystyle = 16x^{2}+ 56xy + 49y^{2}\)

 

Example Question #2 : How To Find The Square Of A Sum

Which of the following is the square of \(\displaystyle 5 \sqrt{x} +3 \sqrt{y}\) ?

You may assume both \(\displaystyle x\) and \(\displaystyle y\) are positive.

Possible Answers:

\(\displaystyle 25x + 9y+ 15\sqrt{xy}\)

\(\displaystyle 5x + 3y+ 15\sqrt{xy}\)

\(\displaystyle 25x + 9y+ 30 \sqrt{xy}\)

\(\displaystyle 25x + 9y\)

\(\displaystyle 5x + 3y+ 30\sqrt{xy}\)

Correct answer:

\(\displaystyle 25x + 9y+ 30 \sqrt{xy}\)

Explanation:

Use the square of a sum pattern, substituting \(\displaystyle 5 \sqrt{x}\) for \(\displaystyle A\) and \(\displaystyle 3 \sqrt{y}\) for \(\displaystyle B\) in the pattern:

\(\displaystyle (A+ B)^{2}= A^{2}+ 2AB + B^{2}\)

\(\displaystyle (5 \sqrt{x}+3 \sqrt{y})^{2}= (5 \sqrt{x})^{2}+ 2 (5 \sqrt{x})\left (3 \sqrt{y} \right ) + \left (3 \sqrt{y} \right )^{2}\)

\(\displaystyle (5 \sqrt{x}+3 \sqrt{y})^{2}= 25x+ 30 \sqrt{xy} + 9y\)

or 

\(\displaystyle 25x + 9y+ 30 \sqrt{xy}\)

Example Question #3 : Square Of Sum

Which of the following is the square of \(\displaystyle x^{2}+ x + 7\) ?

Possible Answers:

\(\displaystyle x^{4}+2x^{3}+8x^{2}+8x+49\)

\(\displaystyle x^{4}+2x^{3}+15x^{2}+14x+49\)

\(\displaystyle x^{4}+ x^{2}+ 49\)

\(\displaystyle x^{4}+ x^{3}+14x^{2}+7x+49\)

\(\displaystyle x^{4}+ x^{3}+14x^{2}+14x+49\)

Correct answer:

\(\displaystyle x^{4}+2x^{3}+15x^{2}+14x+49\)

Explanation:

Multiply vertically as follows:

                    \(\displaystyle \begin{matrix} x^{2}+ \; \; \; x +\; \; \; 7\\\underline{x^{2}+\; \; \; x +\; \; \; 7} \end{matrix}\)

                    \(\displaystyle 7 x^{2}+7 x +49\)

          \(\displaystyle x^{3}+ x^{2} + 7x\)

\(\displaystyle \underline{x^{4}+ x^{3}+7 x^{2} \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; }\)

\(\displaystyle x^{4}+2x^{3}+15x^{2}+14x+49\)

 

Example Question #1 : How To Find The Square Of A Sum

Which of the following is the square of \(\displaystyle y + \sqrt{17}\)  ?

Possible Answers:

\(\displaystyle y^{2}+ 17y+17\)

\(\displaystyle y^{2}+ 34y+17\)

\(\displaystyle y^{2}+ y\sqrt{34}+17\)

The correct answer is not given among the other responses.

\(\displaystyle y^{2}+ y\sqrt{17}+17\)

Correct answer:

The correct answer is not given among the other responses.

Explanation:

Use the square of a sum pattern, substituting \(\displaystyle y\) for \(\displaystyle A\) and \(\displaystyle \sqrt{17}\) for \(\displaystyle B\) in the pattern:

\(\displaystyle (A+ B)^{2}= A^{2}+ 2AB + B^{2}\)

\(\displaystyle (y + \sqrt{17})^{2}= y^{2}+ 2y \sqrt{17} + (\sqrt{17})^{2}\)

\(\displaystyle (y + \sqrt{17})^{2}= y^{2}+ 2y \sqrt{17} + 17\)

This is not equivalent to any of the given choices.

Example Question #3 : Squaring / Square Roots / Radicals

Which of the following is the square of \(\displaystyle \frac{1}{4}x + \frac{1}{7}\) ? 

Possible Answers:

\(\displaystyle \frac{1}{16}x ^{2}+ \frac{1}{56}x +\frac{1}{49}\)

\(\displaystyle \frac{1}{8}x ^{2}+ \frac{1}{28}x +\frac{1}{14}\)

\(\displaystyle \frac{1}{8}x ^{2}+ \frac{1}{14}x +\frac{1}{14}\)

\(\displaystyle \frac{1}{16}x ^{2}+ \frac{1}{14}x +\frac{1}{49}\)

\(\displaystyle \frac{1}{16}x ^{2}+ \frac{1}{28}x +\frac{1}{49}\)

Correct answer:

\(\displaystyle \frac{1}{16}x ^{2}+ \frac{1}{14}x +\frac{1}{49}\)

Explanation:

Use the square of a sum pattern, substituting \(\displaystyle 5 \sqrt{x}\) for \(\displaystyle A\) and \(\displaystyle 3 \sqrt{y}\) for \(\displaystyle B\) in the pattern:

\(\displaystyle (A+ B)^{2}= A^{2}+ 2AB + B^{2}\)

\(\displaystyle \left (\frac{1}{4}x + \frac{1}{7} \right )^{2}= \left (\frac{1}{4}x \right )^{2}+ 2 \left (\frac{1}{4}x \right )\left (\frac{1}{7} \right ) + \left (\frac{1}{7} \right )^{2}\)

\(\displaystyle = \frac{1}{16}x ^{2}+ \frac{1}{14}x +\frac{1}{49}\)

Example Question #2 : Square Of Sum

Which of the following is the square of \(\displaystyle 3.7x + 1.4 y\) ? 

Possible Answers:

\(\displaystyle 7.4x^{2}+ 5.18x y +2.8 y ^{2}\)

\(\displaystyle 13.69x^{2}+ 5.18x y +1.96 y ^{2}\)

\(\displaystyle 7.4x^{2}+ 10.36x y +2.8 y ^{2}\)

\(\displaystyle 13.69x^{2}+ 10.36x y +1.96 y ^{2}\)

\(\displaystyle 13.69x^{2} +1.96 y ^{2}\)

Correct answer:

\(\displaystyle 13.69x^{2}+ 10.36x y +1.96 y ^{2}\)

Explanation:

Use the square of a sum pattern, substituting \(\displaystyle 3.7x\) for \(\displaystyle A\) and \(\displaystyle 1.4 y\) for \(\displaystyle B\) in the pattern:

\(\displaystyle (A+ B)^{2}= A^{2}+ 2AB + B^{2}\)

\(\displaystyle \left (3.7x + 1.4 y \right )^{2}= (3.7x)^{2}+ 2 (3.7x)(1.4 y) + (1.4 y) ^{2}\)

\(\displaystyle = 13.69x^{2}+ 10.36x y +1.96 y ^{2}\)

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