Question

If one root of the quadratic equation \(x^2 +x - 20 = 0\) is 4 then its other root is

(A) 5

(B) -4

(C) -5

(D) 3

Answer 1

Correct option is (C) -5

Let \(\alpha \) and \(\beta\) be the roots of quadratic equation \(x^2 +x - 20 = 0\).

Here,

\(\alpha = 4\)

As we know that,

\(\alpha +\beta = \frac{-b}a\)

\(4 +\beta = \frac{-1}1\)

\(\beta = -1 - 4\)

\(\therefore \beta = -5\)