If -4 is a root of the quadratic equation x^2 + px - 4 = k and the quadratic equation x^2 + px + k = 0 has equal roots, find the value of k.

Question

phi · Answer

and the quadratic equation x^2 + px + k = 0 has equal roots,

are you sure there is no typo?   as stated you get irrational numbers for k.

it works better if this 2nd equation is   x^2 +px -k =0

anonymous · Answer

that is how the question is given in the book
howeverr the answer given is 9/4 !!

phi · Answer

OK, in that case, the typo is in the first equation  (and makes the problem easier)
they must mean
If -4 is a root of the quadratic equation x^2 + px - 4 = 0  (not k)
now you only have to find p, which can be done by substituting x=-4 and solving for p

phi · Answer

once you know p,  you can "complete the square"  to find what k is in the 2nd equation.

anonymous · Answer

@phi 
Thanks !!  I'll try it out and see....