Question

Solve for x:

log_x 81 = 4

Answer 1

Given: log_x 81 = 4

Step-wise calculation: 

By definition of a logarithm,

log_x 81 = 4 means x⁴ = 81. 

81 = 3⁴,

So x⁴ = 3⁴ 

⇒ x = 3 or x = −3.

But the base of a logarithm must be positive and not equal to 1, 

So x = −3 is invalid.