Exercise 40 Page 9

Be careful of wayward negatives!

See solution.

Practice makes perfect

Looking at the erroneous solution, we can see that the mistake was made between Line 2 and Line 3. While multiplying both sides of the equation by 3 using the Multiplication Property of Equality, the negative sign in front of - m3 was lost. Incorrect Line3: & m=- 12 Correct Line3: & - m=- 12 To correct the error, we need to either continue the given solution by dividing both sides of the equation by - 1, or we could multiply the equation by - 3 rather than 3 in Line 2. It may also help to begin solving by moving the negative to the denominator.

-m/3=- 4

MoveNegFracToDenom

Put minus sign in denominator

m/- 3=- 4

MultEqn

LHS * - 3=RHS* - 3

- 3(m/- 3)=- 3(- 4)

FracMultDenomToNumber

a/- 3* - 3 = a

m=- 3(- 4)

MultNegNegOnePar

- a(- b)=a* b