Sometimes we might be given an equation that contains more than one variable and asked to isolate one of the variables. This means that we need to put the variable we're interested in on one side of the equation (on its own) and everything else on the other.
For example, suppose we want to isolate in the equation
The equation has three variables, and However, we will treat the variables and as constants because we are solving for only. We can use the addition and multiplication principles to solve for
First, we add to both sides:
Then, we divide both sides of the equation by
Because the equation is now solved for , we say that we've made the subject of the equation.
Solve for where
We need to isolate so we will treat the other variables and as constants. We can use the addition and multiplication principles to solve for
First, we add to both sides:
Then, we divide both sides by
Make $c$ the subject of the equation $-6a=9b-2c.$
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$c=9b+3a$ |
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$c=\dfrac{9b+6a}{2}$ |
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$c=\dfrac{9b-6a}{2}$ |
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$c=9b+6a+2$ |
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$c=9b+6a-2$ |
The formula for the perimeter of a rectangle is given by $$ p = 2w + 2l, $$
where $w$ is the width of the rectangle and $l$ is the length.
What is the formula for the length of a rectangle in terms of its perimeter and width?
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The energy of a body at rest is related to its mass by the equation , where is a constant. What is an expression for the mass () in terms of the energy () and the constant ()?
We need to isolate so we will treat the other variables and as constants. Since is being multiplied by we need to divide both sides of the equation by : Thus,
Note: This result assumes that
The average velocity of a body in free fall is given by $$ v = \dfrac{1}{2}gt, $$
where $g$ is gravity and $t$ is the time that the body has fallen.
What is the formula for the time in terms of the other variables?
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$t= 2v - g$ |
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$t= \dfrac{g}{2v}$ |
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$t= 2vg$ |
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$t= \dfrac{2v}{g}$ |
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$t= 2v + g$ |
The total energy of a body moving with a (squared) velocity can be approximated using the equation Find an expression for in terms of the other quantities.
We need to isolate so we will treat the other variables and as constants. We can use the addition and multiplication principles to solve for
First, we subtract from both sides of the equation:
Then, we multiply by to get rid of the fraction:
Finally, we divide by to get alone:
Thus,
Note: This result assumes that
If $5cd = a+b,$ then $c = $
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If $\dfrac{pq}{4} - 2r = 5p,$ then $q = $
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A company calculates each employee's monthly salary using the formula $$ s = b+rh, $$
where $b$ is the base salary (which is fixed regardless of the number of overtime hours worked), $r$ is the hourly rate for overtime work, and $h$ is the number of overtime hours worked.
What is the formula for the number of overtime hours worked in terms of the other variables?
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