Question

What is the value of x, when x2 + 5 = 21? A) 2 or -2 B) 4 or -4 C) 5.5 or -5.5 Eliminate D) 8 or -8

Answer 1

2x +5=21
2x= 21-5
x= 16/2
x= 8
So , the write answer is D) 8 or - 8

Answer 2

Ans.

${x}^{2} + 5 = 21 \\ or \: {x}^{2} - 16= 0\\ or \: (x + 4)(x - 4) = 0 \\ \\ so \: \: \: x = - 4 \: and \: x = 4$

Hence, option (B) is correct.