Question

Find the value of k such that when 2x^3+9x^2+kx-15 is divided by x+5, the remainder is 0.

Answer 1

If I can remember correctly..
My solution is:
x + 5 = 0
x = -5
substitute -5 to x then solve for k.
Use the remainder 0 in the left hand/right hand side of the equation.
2x^3+9x^2+kx-15 = 0 (The remainder)
2(-5)^3 + 9(-5)^2 + k (-5) - 15 = 0
-250 + 225 - 15 - 5k = 0
85 - 5k = 0
-5k = -85
5k = 85
k = 17