If one root of the equation 2x2+3x-k=0 is 6, what is the value of k?
A
90
B
42
C
18
D
10
Correct Answer: 90
When we have a value of one root in a quadratic equation, make the RHS to zero (0) so that we can substitute the given root to find the other variables. In this case, the RHS is already 0. So just substitute the given root value for x, i.e, x = 6 = > 2×6² + 3×(6) - k = 0 = > 2×(36) + 18 = k = > 72 + 18 = k ∴ k = 90