Question

Solve for x. x2 + 4x - 21 = 0 A. -3, -7 B. -3, 7 C. 3, -7 D. 3, 7

Answer 1

Please, use " ^ " to denote exponentiation: x^2 + 4x - 21 = 0

Factor: (x+7)(x-3)=0

Solve for the 2 roots: x= -7 and x= 3: {3, -7} Note how this is in set notation.

Answer 2

Answer:  the correct option is

(C) 3, -7.

Step-by-step explanation:  We are given to solve the following equation for x :

$x^2+4x-21=0~~~~~~~~~~~~~~~~~~~~~~~```(i)$

We will be solving the given quadratic equation by factorization.

The solution of equation (i) is as follows :

$x^2+4x-21=0\\\\\Rightarrow x^2+7x-3x-21=0\\\\\Rightarrow x(x+7)-3(x+7)=0\\\\\Rightarrow (x-3)(x+7)=0\\\\\Rightarrow x-3=0,~~~x+7=0\\\\\Rightarrow x=3,~-7.$

Thus, the required values of x are

x = 3, -7.

Option (C) is CORRECT.