f(x)=6

fx)=20+2x^2 all under a square root symbol

6=20+2(36)
6=the square root of 92

will someone help me

f(x) = y = 6

y = sqrt(20 + 2 x^2)
6 = sqrt(20 + 2 x^2)
square both sides but check in the end for which solution works
36 = 20 + 2 x^2
8 = x^2
x = + 2sqrt 2 or -2 sqrt 2

check x = +2 sqrt 2
6 = sqrt ( 20 + 16) yes
check x = -2 sqrt 2
6 = sqrt (20+16) yes