Question

if log(x^2 - 21) =2 show that x= +-11

Answer 1

log(x²-21)=2

10^2=x²-21 (writing the logarithm in exponential form)

x²-21=100

x²=100+21

x²=121

x=√121=±11

Answer 2

Hey
Here's your answer !!

log ( x^2 - 21 ) = 2
=> log ( x^2 - 21 ) = log 100
Taking anti logarithm both sides ,
=> ( x^2 - 21 ) = 100
=> x^2 = 100 + 21
=> x^2 = 121
=> x = +- 11 . ( proved )

Hope it helps !!