I know this is probably really easy, but i just can't figure it out..
Homework Statement
Find values of k for which (5 + 4x - x^2 = k) has equal roots.
I know the answer is k = 9 but i don't know how to get there..
Homework Equations
ax^2 + bx + c = 0
Discriminant = b^2 - 4ac...