1. 3-8 Solving Equations and Formulas
Objectives: Students will solve equations for given variables and use formulas to solve real-world problems.
S. Calahan
2008

2. Solve an equation for a Specific Variable
When an equation contains more than one variable you may need to solve the equation for one of the variables.
3x – 4y = 7 solve for y
So we need to subtract 3x from each side of the equation to leave the y term by itself.
11/16/2018

3. 3x – 4y = 7 -3x = -3x -4y = -3x + 7 -4 -4 y = -3x + 7 -4
y = -3x + 7 -4
The value of y is -3x + 7
11/16/2018

4. Solve an equation for a specific variable
2m – t = sm + 5 solve for m
In a problem like this we must first isolate the variable m since that is the variable we are solving for.
2m – t = sm + 5
-sm sm
2m – sm – t = 5
Remember: sm and 2m are NOT like terms.
11/16/2018

5. 2m – sm – t = 5 2m –sm – t + t = 5 + t 2m – sm = 5 + t
To isolate the m terms we must add t to both sides.
2m –sm – t + t = 5 + t
2m – sm = 5 + t
m(2 – s) = 5 + t use the distributive property
2 – s – s to isolate m
m = 5 + t
2 – s Divide both sides by 2 - s
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6. Use a formula C = 2πr C = circumference r = radius
If the circumference of a ball is
24 inches what is the radius?
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7. First solve the formula for r
C = 2πr divide both sides by 2π
2π 2π
r = C 2π
Now substitute c = 24 and solve for the radius
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8. r = C π
r = 24/2π remember π = 3.14
= in.
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