Posted by Rachal on Tuesday, February 15, 2011 at 11:09pm.
Solve for x.
log3(x+7)=2log3(x1)
Write the exact answer using base10 logarithms.

Math  Reiny, Tuesday, February 15, 2011 at 11:21pm
log3(x+7)=2log3(x1)
log3(x+7) + log3(x1) = 2
log3 [(x+7)/(x1)] = 2
(x+7)(x1) = 3^2
x^2 + 6x  7 = 9
x^2 + 6x  16 = 0
(x+8)(x2) = 0
x = 8 or x = 2
but x=8 would make log3(x+7) undefined, so
x = 2
( why would it ask to use base 10 logs ????)