Question

If one root of the quadratic equation \(x^2 + 2kx + 4 = 0\) is 2, then value of k is

(A) -1

(B) -2

(C) 2

(D) -4

Answer 1

Correct option is (B) -2

Given,

\( f(x)=x^{2}+2 k x+4\)

\(x=2\)

\(P(x)=x^{2}+2 k x+4=0\)

\(\Rightarrow(2)^{2}+2 k \cdot 2+4=0 \)

\(4+4 k+4=0\)

\( 4 k+8=0\)

\(4 k=-8\)

\( \therefore k=\frac{-8}{4}=-2\)