Undefined control sequence \dpi

PSAT Math : How to find the common factors of squares

Study concepts, example questions & explanations for PSAT Math

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Example Questions

Example Question #1 : Factoring And Simplifying Square Roots

Solve for \dpi{100} x:

x\sqrt{45}+x\sqrt{72}=\sqrt{18}\displaystyle x\sqrt{45}+x\sqrt{72}=\sqrt{18}

Possible Answers:

x=\sqrt{9}\displaystyle x=\sqrt{9}

x=\frac{\sqrt{2}}{\sqrt{5}}+\frac{1}{2}\displaystyle x=\frac{\sqrt{2}}{\sqrt{5}}+\frac{1}{2}

x=3\displaystyle x=3

x=\frac{\sqrt{5}}{\sqrt{2}}+2\displaystyle x=\frac{\sqrt{5}}{\sqrt{2}}+2

x=\frac{\sqrt{2}}{\sqrt{5}+2\sqrt{2}}\displaystyle x=\frac{\sqrt{2}}{\sqrt{5}+2\sqrt{2}}

Correct answer:

x=\frac{\sqrt{2}}{\sqrt{5}+2\sqrt{2}}\displaystyle x=\frac{\sqrt{2}}{\sqrt{5}+2\sqrt{2}}

Explanation:

x\sqrt{45}+x\sqrt{72}=\sqrt{18}\displaystyle x\sqrt{45}+x\sqrt{72}=\sqrt{18}

Notice how all of the quantities in square roots are divisible by 9

x\sqrt{9\times 5}+x\sqrt{9\times 8}=\sqrt{9\times 2}\displaystyle x\sqrt{9\times 5}+x\sqrt{9\times 8}=\sqrt{9\times 2}

x\sqrt{9}\sqrt{5}+x\sqrt{9}\sqrt{4\times 2}=\sqrt{9}\sqrt{2}\displaystyle x\sqrt{9}\sqrt{5}+x\sqrt{9}\sqrt{4\times 2}=\sqrt{9}\sqrt{2}

3x\sqrt{5}+3x\sqrt{4}\sqrt{2}=3\sqrt{2}\displaystyle 3x\sqrt{5}+3x\sqrt{4}\sqrt{2}=3\sqrt{2}

3x\sqrt{5}+6x\sqrt{2}=3\sqrt{2}\displaystyle 3x\sqrt{5}+6x\sqrt{2}=3\sqrt{2}

x(3\sqrt{5}+6\sqrt{2})=3\sqrt{2}\displaystyle x(3\sqrt{5}+6\sqrt{2})=3\sqrt{2}

x=\frac{3\sqrt{2}}{3\sqrt{5}+6\sqrt{2}}\displaystyle x=\frac{3\sqrt{2}}{3\sqrt{5}+6\sqrt{2}}

Simplifying, this becomes

x=\frac{\sqrt{2}}{\sqrt{5}+2\sqrt{2}}\displaystyle x=\frac{\sqrt{2}}{\sqrt{5}+2\sqrt{2}}

Example Question #2 : Factoring And Simplifying Square Roots

If m and n are postive integers and 4m = 2n, what is the value of m/n?

Possible Answers:

2

1/2

16

4

8

Correct answer:

1/2

Explanation:
  1. 2= 4. Also, following the rules of exponents, 4= 1. 
  2. One can therefore say that m = 1 and n = 2.
  3. The question asks to solve for m/n. Since m = 1 and n = 2, m/n = 1/2.

Example Question #3 : Factoring And Simplifying Square Roots

Simplify the radical:

\displaystyle \sqrt{320}

Possible Answers:

\displaystyle \sqrt{320}

\displaystyle 4\sqrt{20}

\displaystyle 8\sqrt{5}

\displaystyle 8\sqrt{20}

\displaystyle 4\sqrt{5}

Correct answer:

\displaystyle 8\sqrt{5}

Explanation:

\displaystyle \sqrt{320}=\sqrt{2\times 160}=\sqrt{2\times 2\times 80}=2\sqrt{80}=2\sqrt{2\times 40}=2\sqrt{2\times 2\times 20}=2\times 2\times \sqrt{20}=4\sqrt{2\times 10}=4\sqrt{2\times 2\times 5}=4\times 2\times \sqrt{5}=8\sqrt{5}

 

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