If -5 is a root of the quadratic equation 2x2 + px – 15 = 0 and the quadratic equation p(x2 + x)k = 0 has equal roots, find the value of k.
We Given -5 is a root of the quadratic equation 2x2+px-15 =0
, -5 satisfies the given equation.
∴ 2 (-5)2 +p(-5)-15=0
50-5p-15 =0
35-5p=0
5p=35 ⇒ p=7
Substituting p=7 in (x2+x)+k =0, we get
7(x2+x)+k =0
7x2+7x+k=0
The roots of the equation are equal
∴ Discriminant =b2-4ac =0
Here, a= 7, b=7,c=k
b2-4ac=0
∴(7)2-4(7)(k) =0
49-28k =0
28k=49
k= 49/28
=7/4