Algebra
Class 9-11

Logarithm Laws

loga(xy)=logax+logay\log_a(xy) = \log_a x + \log_a y
20406080100−1−0.500.511.52
log(xy) = log(x) + log(y)

Adjust Variables

Base
base =
210

Logarithms convert multiplication to addition. Other laws: log(x/y) = log(x) - log(y), log(xⁿ) = n×log(x).

Real-World Applications

Earthquake magnitude — Richter scale: each unit is 10× more energy (logarithmic).

Sound decibels — dB = 10×log(I/I₀); logarithmic perception of loudness.

pH scale — pH = -log[H⁺]; each unit is 10× change in acidity.

Stellar magnitude — Apparent magnitude is logarithmic; 5 units = 100× brightness difference.

Data compression — Information theory uses log₂ for bits.

Algorithm complexity — O(log n) means doubling input adds one step.

Radioactive dating — Age = (1/λ)×ln(N₀/N); solving exponential decay.

Music intervals — Octaves are logarithmic; each doubles frequency.

Population growth — Doubling time = ln(2)/r.

Slide rules — Historical calculators used log scales for multiplication.

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