Question

What are the possible values for x in the equation 4x^2 = 64

(1) x=0        (2) x=4       (3) x=4,-4      (4) x=0,4,-4

Answer 1

4x^2 = 64

1)
4(0^2) = 64
4(0) = 64
0 = 64
Not True

2)
4(4^2) = 64
4(16) = 64
64 = 64
True

3)
4(4^2) = 64
4(16) = 64
64 = 64
4(-4^2) = 64
4(16) = 64
64 = 64
True

4)
4(4^2) = 64
4(16) = 64
64 = 64
4(-4^2) = 64
4(16) = 64
64 = 64
4(0^2) = 64
4(0) = 64
0 = 64
Not True

Answer: (3)

Answer 2

$4x^2 = 64\ \ /:4 \\ \\x^2=16 \\ \\ x^2-16=0 \\ \\x^2-4^2=0\\ \\ (x-4)(x+4)=0\\ \\x-4=0 \ \ or \ \ x+4=0 \\ \\ x=4 \ \ or \ \ x= -4 \\ \\ Answer : \ (3)$