CALCULATIONS INVOLVING LOGARITHMS
Because logarithms are exponents, mathematical operations involving them follow the same rules as those for exponents.
Common Logarithm | Natural Logarithm |
---|---|
log xy = log x + log y | Ln xy = Ln x + Ln y |
log x/y = log x - log y | Ln x/y = Ln x - Ln y |
log xy = y log x | Ln xy = y Ln x |
log y√x = log x1/y = (1/y )log x | Ln y√x = Ln x1/y =(1/y)Ln x |
- Example 9: log 5.0 x 106 = log 5.0 + log 106 = 0.70 + 6 = 6.70
Hint: This is an easy way to estimate the log of a number in scientific notation! - Example 10: log (154/25) = log 154 - log 25 = 2.188 - 1.40 = 0.788 = 0.79 (2 sig. fig.)
- Example 11: log (5.46 x 10-3)6 = 6 log 5.46 x 10-3 = 6 x (-2.263) = -13.58
- Example 12: log (4.35)1/4 = 1/4 log 4.35 = 0.160