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How Do You Solve an Equation Using Division?
Solve -3b = -21 for b
Summary
- 'b' is a variable
- Solve for 'b' by dividing both sides by -3
- The -3's cancel out on the left
- And -21 divided by -3 is 7
- A negative number divided by another negative number has a positive quotient
- Plug 7 in our original equation for b to check the answer
- -3 times 7 is -21, so both sides are equal

Notes
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- 'b' is a variable
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- The opposite of multiplication is division
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- In our case, we are dividing both sides by -3
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- This is an aspect of the division property of equality
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- The division property of equality tells us that if we divide one side by something, then we have to divide the other side by the same thing
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- -3b divided by -3 is just 'b'
- -21 divided by -3 is equal to 7
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- b=7 is our answer!
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- Plug 7 in the original equation for 'b'
- Then evaluate the equation to see if our answer is correct
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- Put a 7 everywhere you see a 'b'
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- Now evaluate the expression
- -3 times 7 is equal to -21
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- We checked our answer by plugging it back into the original equation
- We have a true statement after plugging in our answer, so our answer is correct!
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- We checked our answer by plugging it back into the original equation
- We have a true statement after plugging in our answer, so our answer is correct!