Homework Help: Precalculus

Posted by Lea on Monday, January 30, 2012 at 11:39pm.

1.Solve 5^(2x) -4(5^x)=12

2. Solve Log[8](log[8]x)=0

Precalculus - Reiny, Tuesday, January 31, 2012 at 12:43am
let 5^x = y , then we have

y^2 - 4y - 12 = 0
(y-6)(x+2) = 0
y = 6 or y = -2

5^x = 6
xlog5 = log6
x = log6/log5 = appr. 1.1133
or
5^x = -2
xlog5 = log (-2), but we cannot take logs of negatives, so no solution for that case

x = log6/log5 or 1.1133

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