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.