Question

Solve |5x + 15| = 10x. Identify the solution and an extraneous solution.

A. Solution: x= 3; extraneous solution: x=-3
B. Solution: x= 3; extraneous solution: X=-1
c. Solution: x= 1; extraneous solution: X=-3
D. Solution: ×= -1; extraneous solution: X=3

Answer 1

If 5x + 15 ≥ 0, then |5x + 15| = 5x + 15. The equation reduces to

5x + 15 = 10x

15 = 5x

x = 3

If instead 5x + 15 < 0, then |5x + 15| = -(5x + 15), and the equation becomes

-5x - 15 = 10x

-15 = 15x

x = -1

If x = 3, then |5x + 15| = 30 and 10x = 30, so x = 3 is a valid solution.

If x = -1, then |5x + 15| = 10 while 10x = -10, so x = -1 is the extraneous solution.