ACT Preparation / Unit 12 ACT 1118 short lesson, about 20 seconds
Solving With Logarithms
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The idea
When no common base exists, isolate the exponential expression, take the log of both sides, and use the power rule to bring the exponent down.
In practice
3ˣ = 20 gives x log 3 = log 20, so x = log 20 / log 3, about 2.73.
Where people slip
Isolate first: in 5 · 3ˣ = 100, divide by 5 before taking logs.
Your place on the trail
Every lesson rests on earlier ones and opens later ones. Tap any to jump.
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