ACT Preparation / Unit 12 ACT 1111 short lesson, about 20 seconds
Common and Natural Logarithms
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The idea
The common logarithm, log x, has base 10. The natural logarithm, ln x, has base e. Both follow the same definition and rules.
In practice
log 1,000 = 3, because 10³ = 1,000; log 0.01 = −2; ln e⁵ = 5.
Where people slip
A log written with no base means base 10; ln always means base e.
Your place on the trail
Every lesson rests on earlier ones and opens later ones. Tap any to jump.
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