Question 170597: ln (y^2-1)= ln(y-1) + ln5
Answer by nerdybill(7384)   (Show Source):
You can put this solution on YOUR website! Using "log rules":
ln (y^2-1)= ln(y-1) + ln5
ln (y^2-1)= ln(5(y-1))
ln (y^2-1)= ln(5y-5)
y^2-1= 5y-5
y^2-5y-1= -5
y^2-5y+4= 0
Factoring:
(y-4)(y-1)= 0
y = {1,4}
You have to toss out 1 as a possible solution since ln(0) is undefined.
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Therefore:
y = 4
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