PSAT Math : How to find the square of a sum

Study concepts, example questions & explanations for PSAT Math

varsity tutors app store varsity tutors android store

Example Questions

Example Question #1 : Squaring / Square Roots / Radicals

Simplify the radical.

\sqrt{3283}\(\displaystyle \sqrt{3283}\)

Possible Answers:

7\sqrt{67}\(\displaystyle 7\sqrt{67}\)

7\sqrt{63}\(\displaystyle 7\sqrt{63}\)

57.3\(\displaystyle 57.3\)

67\sqrt{49}\(\displaystyle 67\sqrt{49}\)

56\(\displaystyle 56\)

Correct answer:

7\sqrt{67}\(\displaystyle 7\sqrt{67}\)

Explanation:

We can break the square root down into 2 roots of 67 and 49. 49 is a perfect square and reduces to 7.

Example Question #61 : Exponents

Expand:

\(\displaystyle \left ( 10x+ \frac{1}{5}\right )^{2}\)

Possible Answers:

\(\displaystyle 100x^{2} + \frac{1}{25}\)

\(\displaystyle 100x^{2} + \frac{1}{10}\)

\(\displaystyle 100x^{2} + 2x + \frac{1}{25}\)

\(\displaystyle 100x^{2} + 4x + \frac{1}{25}\)

\(\displaystyle 100x^{2} + 2x + \frac{1}{10}\)

Correct answer:

\(\displaystyle 100x^{2} + 4x + \frac{1}{25}\)

Explanation:

Use the perfect square trinomial pattern, setting \(\displaystyle A = 10x , B = \frac{1}{5}\):

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

\(\displaystyle \left ( 10x + \frac{1}{5} \right )^{2} = (10x)^{2} + 2 (10x) \left ( \frac{1}{5} \right ) + \left ( \frac{1}{5} \right ) ^{2}\)

\(\displaystyle = 100x^{2} + 4x + \frac{1}{25}\)

Example Question #3 : How To Find The Square Of A Sum

If \(\displaystyle \left (5 x^{2 } - x + 1\right )^{2}\) is expanded, what is the coefficient of \(\displaystyle x^{2}\) ?

Possible Answers:

\(\displaystyle 4\)

\(\displaystyle 9\)

\(\displaystyle 11\)

\(\displaystyle 6\)

There is no \(\displaystyle x^{2}\) term in the expansion of \(\displaystyle \left (5 x^{2 } - x + 1\right )^{2}\).

Correct answer:

\(\displaystyle 11\)

Explanation:

\(\displaystyle \left (5 x^{2 } - x + 1\right )^{2}\)

\(\displaystyle = \left (5 x^{2 } - x + 1\right ) \left (5 x^{2 } - x + 1\right )\)

\(\displaystyle = 5 x^{2 } \left (5 x^{2 } - x + 1\right ) - x \left (5 x^{2 } - x + 1\right ) + 1 \left (5 x^{2 } - x + 1\right )\)

\(\displaystyle = 5 x^{2 } \cdot 5 x^{2 } - 5 x^{2 } \cdot x + 5x^{2 } \cdot 1 - x \cdot 5 x^{2 }+ x \cdot x - x \cdot 1+ 1\cdot 5 x^{2 } - 1 \cdot x + 1\cdot 1\)

\(\displaystyle = 25 x^{4 } - 5 x^{3 } + 5x^{2 } - 5 x^{3 }+ x ^{2 } - x + 5 x^{2 } - x + 1\)

\(\displaystyle = 25 x^{4 } - 5 x^{3 } - 5 x^{3 } + 5x^{2 }+ 5 x^{2 } + x ^{2 } - x - x + 1\)

\(\displaystyle = 25 x^{4 } -10 x^{3 } + 11 x^{2 } -2 x + 1\)

The coefficient of \(\displaystyle x^{2}\) is therefore 11.

Example Question #503 : Algebra

If \(\displaystyle \left (5 x^{2 } - x + 1\right )^{2}\) is expanded, what is the coefficient of \(\displaystyle x^{3}\) ?

Possible Answers:

\(\displaystyle 10\)

\(\displaystyle 2\)

\(\displaystyle 1\)

There is no \(\displaystyle x^{3}\) term in the expansion of \(\displaystyle \left (5 x^{2 } - x + 1\right )^{2}\).

\(\displaystyle 5\)

Correct answer:

\(\displaystyle 10\)

Explanation:

\(\displaystyle \left (5 x^{2 } - x + 1\right )^{2}\)

\(\displaystyle = \left (5 x^{2 } - x + 1\right ) \left (5 x^{2 } - x + 1\right )\)

\(\displaystyle = 5 x^{2 } \left (5 x^{2 } - x + 1\right ) - x \left (5 x^{2 } - x + 1\right ) + 1 \left (5 x^{2 } - x + 1\right )\)

\(\displaystyle = 5 x^{2 } \cdot 5 x^{2 } - 5 x^{2 } \cdot x + 5x^{2 } \cdot 1 - x \cdot 5 x^{2 }+ x \cdot x - x \cdot 1+ 1\cdot 5 x^{2 } - 1 \cdot x + 1\cdot 1\)

\(\displaystyle = 25 x^{4 } - 5 x^{3 } + 5x^{2 } - 5 x^{3 }+ x ^{2 } - x + 5 x^{2 } - x + 1\)

\(\displaystyle = 25 x^{4 } - 5 x^{3 } - 5 x^{3 } + 5x^{2 }+ 5 x^{2 } + x ^{2 } - x - x + 1\)

\(\displaystyle = 25 x^{4 } -10 x^{3 } + 11 x^{2 } -2 x + 1\)

The coefficient of \(\displaystyle x^{3}\) is therefore 10.

Example Question #3 : Squaring / Square Roots / Radicals

Expand:

\(\displaystyle \left ( 10x+ 0.8\right )^{2}\)

Possible Answers:

\(\displaystyle 100x^{2} + 1.6x + 6.4\)

\(\displaystyle 100x^{2}+8x + 0.64\)

\(\displaystyle 100x^{2} + 16x + 0.64\)

\(\displaystyle 100x^{2} +0. 16x + 0.064\)

\(\displaystyle 100x^{2} +0.8x+ 6.4\)

Correct answer:

\(\displaystyle 100x^{2} + 16x + 0.64\)

Explanation:

Use the perfect square trinomial pattern, setting \(\displaystyle A = 10x , B = 0.8\):

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

\(\displaystyle (10x + 0.8)^{2} = \left (10x \right )^{2} + 2 \cdot 10x \cdot 0.8 + 0.8^{2}\)

\(\displaystyle (10x + 0.8)^{2} = 100x^{2} + 16x + 0.64\)

Learning Tools by Varsity Tutors