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How Do You Solve an Equation Using Division?

Solve -3b = -21 for b

Summary

  1. 'b' is a variable
  2. Solve for 'b' by dividing both sides by -3
  3. The -3's cancel out on the left
  4. And -21 divided by -3 is 7
  5. A negative number divided by another negative number has a positive quotient
  6. Plug 7 in our original equation for b to check the answer
  7. -3 times 7 is -21, so both sides are equal

Notes

    1. 'b' is a variable
    1. The opposite of multiplication is division
    1. In our case, we are dividing both sides by -3
    1. This is an aspect of the division property of equality
    1. 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
    1. -3b divided by -3 is just 'b'
    2. -21 divided by -3 is equal to 7
    1. b=7 is our answer!
    1. Plug 7 in the original equation for 'b'
    2. Then evaluate the equation to see if our answer is correct
    1. Put a 7 everywhere you see a 'b'
    1. Now evaluate the expression
    2. -3 times 7 is equal to -21
    1. We checked our answer by plugging it back into the original equation
    2. We have a true statement after plugging in our answer, so our answer is correct!
    1. We checked our answer by plugging it back into the original equation
    2. We have a true statement after plugging in our answer, so our answer is correct!