• The logarithmic function is the inverse of the exponential function. We write:

y = loga x if and only if x = ay

• where a > 0, a ≠ 1, and x > 0.
• The expression is read “log base a of x”, and it means the exponent to which we raise the base a to get x.
• For example, log₂ 8 = 3 because 2³ = 8. Also log₁₀ 0.01 = −2 because 10⁻² = 0.01.
• When no base is written, the base is 10 by convention, so log x means log₁₀ x.