HiSET: Math : Rearrange formulas/equations to highlight a quantity of interest

Study concepts, example questions & explanations for HiSET: Math

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Example Questions

Example Question #1 : Rearrange Formulas/Equations To Highlight A Quantity Of Interest

Solve for \displaystyle x:

\displaystyle \frac{2x+3y }{c} = 20

Possible Answers:

\displaystyle x =10 c -\frac{3}{2} y

\displaystyle x =40 c -\frac{3}{2} y

\displaystyle x =40 c - 3y

\displaystyle x =20 c -\frac{3}{2} y

\displaystyle x =10 c -3 y

Correct answer:

\displaystyle x =10 c -\frac{3}{2} y

Explanation:

To solve for \displaystyle x in a literal equation, use the properties of algebra to isolate \displaystyle x on one side, just as if you were solving a regular equation. 

\displaystyle \frac{2x+3y }{c} = 20

Multiply both sides by \displaystyle c:

\displaystyle \frac{2x+3y }{c} \cdot c = 20 \cdot c

\displaystyle 2x+3y = 20 c

Subtract \displaystyle 3y from both sides:

\displaystyle 2x+3y - 3y = 20 c - 3y

\displaystyle 2x = 20 c - 3y

Multiply both sides by \displaystyle \frac{1}{2}, distributing on the right:

\displaystyle \frac{1}{2} \cdot 2x =\frac{1}{2} \cdot (20 c - 3y)

\displaystyle x =\frac{1}{2} \cdot 20 c -\frac{1}{2} \cdot 3y

\displaystyle x =10 c -\frac{3}{2} y,

the correct response.

 

Example Question #21 : Algebraic Concepts

Solve for \displaystyle x:

\displaystyle 9x^{2}+z = y

Assume \displaystyle x is positive.

Possible Answers:

\displaystyle x = 3 \sqrt {y - z}

\displaystyle x = \frac{\sqrt {y - z}}{3}

\displaystyle x = \sqrt {3y - 3z}

\displaystyle x = 9 \sqrt {y - z}

\displaystyle x = \frac{\sqrt {y - z}}{9}

Correct answer:

\displaystyle x = \frac{\sqrt {y - z}}{3}

Explanation:

To solve for \displaystyle x in a literal equation, use the properties of algebra to isolate \displaystyle x on one side, just as if you were solving a regular equation. 

\displaystyle 9x^{2}+z = y

Subtract \displaystyle z from both sides:

\displaystyle 9x^{2}+z - z = y - z

\displaystyle 9x^{2} = y - z

Divide both sides by 9:

\displaystyle \frac{9x^{2}}{9} = \frac{y - z}{9}

\displaystyle x^{2} = \frac{y - z}{9}

Take the square root of both sides:

\displaystyle x =\sqrt{ \frac{y - z}{9}}

Simplify the expression on the right by splitting it, and taking the square root of numerator and denominator:

\displaystyle x = \frac{\sqrt {y - z}}{\sqrt {9}}

\displaystyle x = \frac{\sqrt {y - z}}{3},

the correct response.

Example Question #1 : Rearrange Formulas/Equations To Highlight A Quantity Of Interest

Solve for \displaystyle x:

\displaystyle \frac{y+1}{x+1} = 3

Possible Answers:

\displaystyle x = \frac{2}{3} y + \frac{1}{3}

\displaystyle x = \frac{4}{3} y + \frac{1}{3}

\displaystyle x = \frac{2}{3} y -\frac{4}{3}

\displaystyle x = \frac{1}{3} y - \frac{2}{3}

\displaystyle x = \frac{1}{3} y + \frac{4}{3}

Correct answer:

\displaystyle x = \frac{1}{3} y - \frac{2}{3}

Explanation:

To solve for \displaystyle x in a literal equation, use the properties of algebra to isolate \displaystyle x on one side, just as if you were solving a regular equation. 

First, take the reciprocal of both sides:

\displaystyle \frac{y+1}{x+1} = 3

\displaystyle \frac{x+1}{y+1} = \frac{1}{3}

Multiply both sides by \displaystyle y+1:

\displaystyle \frac{x+1}{y+1} \cdot (y+1)= \frac{1}{3}(y+1)

\displaystyle x+1= \frac{1}{3}(y+1)

Distribute on the right:

\displaystyle x+1= \frac{1}{3} \cdot y+ \frac{1}{3} \cdot 1

\displaystyle x+1= \frac{1}{3} y+ \frac{1}{3}

Subtract 1 from both sides, rewriting 1 as \displaystyle \frac{3}{3} to facilitate subtraction:

\displaystyle x+1 - 1 = \frac{1}{3} y+ \frac{1}{3} - 1

\displaystyle x = \frac{1}{3} y+ \frac{1}{3} - \frac{3}{3}

\displaystyle x = \frac{1}{3} y - \frac{2}{3},

the correct response.

 

Example Question #2 : Rearrange Formulas/Equations To Highlight A Quantity Of Interest

Solve for \displaystyle x:

\displaystyle xy+20 = z

Possible Answers:

\displaystyle x= \frac{z - 20y}{y}

\displaystyle x= \frac{yz - 20}{y}

\displaystyle x= z - 20y

\displaystyle x= \frac{z - 20}{y}

\displaystyle x=yz - 20

Correct answer:

\displaystyle x= \frac{z - 20}{y}

Explanation:

To solve for \displaystyle x in a literal equation, use the properties of algebra to isolate \displaystyle x on one side, just as if you were solving a regular equation. 

\displaystyle xy+20 = z

Subtract 20 from both sides:

\displaystyle xy+20- 20 = z - 20

\displaystyle xy = z - 20

Divide both sides by \displaystyle y:

\displaystyle \frac{xy}{y} = \frac{z - 20}{y}

\displaystyle x= \frac{z - 20}{y},

the correct response.

Example Question #251 : Hi Set: High School Equivalency Test: Math

Solve for \displaystyle x:

\displaystyle 32 -x^{2} = y

You my assume \displaystyle x is positive.

Possible Answers:

\displaystyle x=\sqrt{ y - 32}

\displaystyle x=\sqrt{ y}- 32

\displaystyle x=\sqrt{ y^{2}- 32}

\displaystyle x=\sqrt{ 32- y}

\displaystyle x=\sqrt{ 32}- y

Correct answer:

\displaystyle x=\sqrt{ 32- y}

Explanation:

To solve for \displaystyle x in a literal equation, use the properties of algebra to isolate \displaystyle x on one side, just as if you were solving a regular equation. 

First, add \displaystyle x^{2} - y to both sides:

\displaystyle 32 -x^{2} +(x^{2} - y) = y +(x^{2} - y)

\displaystyle 32 -x^{2} +x^{2} - y = x^{2} +y - y

\displaystyle 32 - y = x^{2}

Take the positive square root of both sides:

\displaystyle x=\sqrt{ 32- y},

the correct response.

Example Question #1 : Rearrange Formulas/Equations To Highlight A Quantity Of Interest

Solve for \displaystyle x:

\displaystyle \sqrt{x+1}= y+1

Possible Answers:

\displaystyle x = y^{2}+ y

\displaystyle x = y^{2}-2 y

\displaystyle x = y^{2}- y

\displaystyle x = y^{2}+ 2 y

\displaystyle x = y^{2}

Correct answer:

\displaystyle x = y^{2}+ 2 y

Explanation:

To solve for \displaystyle x in a literal equation, use the properties of algebra to isolate \displaystyle x on one side, just as if you were solving a regular equation. 

First, square both sides to eliminate the radical symbol:

\displaystyle \sqrt{x+1}= y+1

\displaystyle (\sqrt{x+1})^{2}=( y+1)^{2}

\displaystyle x+1=( y+1)^{2}

Rewrite the expression on the right using the square of a binomial pattern:

\displaystyle x+1= y^{2}+ 2 (y)(1)+1^{2}

\displaystyle x+1= y^{2}+ 2 y+1

Subtract 1 from both sides:

\displaystyle x+1-1 = y^{2}+ 2 y+1 - 1

\displaystyle x = y^{2}+ 2 y,

the correct response.

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