Quadratic Polynomial Problem/s (1 Viewer)

[biggie walls]

Hi can someone please show me how to do this question, its to do with the discriminant...

Find values of k for which 5 + 4x - x^2 = k has equal roots.

I know that for equal roots the discriminant = 0

but that equation has me dumbfounded...

apparantly the answer is k=9

Thanks in advance

 

[2006]

b^2 - 4ac = 0
(-4)^2 - 4(1)(k-5) = 0
16 - 4k + 20 = 0
4k = 36
k = 9

 

[Riviet]

Just a little explanation:
Bring everything on one side and you get:
x²-4x+k-5=0, where a=1, b=-4, c=k-5
Then sub. into b²-4ac=0 and solve for k, which 2006 has done for you.

 

[biggie walls]

Cheers!