How do you solve this logarithmic function?

Question

#(16/25)^(x+3)=(125/64)^(x-1)#

2081 views around the world

You can reuse this answer
Creative Commons License

Answer 1 · 2016-11-17T23:29:49

Please see the explanation.

Use either the natural or base 10 logarithm on both sides. (I will use the natural logarithm):

#ln((16/25)^(x+3)) = ln((125/64)^(x-1))#

Use the property of all logarithms #log_b(a^c) = (c)log_b(a)#:

#(x+3)ln(16/25) = (x-1)ln(125/64)#

Use the distributive property on both sides:

#(x)ln(16/25) + (3)ln(16/25) = (x)ln(125/64) -ln(125/64)#

Move the x terms to the left and the constant terms to the right:

#(x)ln(16/25) - (x)ln(125/64) = - (3)ln(16/25) - ln(125/64)#

Factor out x on the left:

#(x)(ln(16/25) - ln(125/64)) = - (3)ln(16/25) - ln(125/64)#

Divide both sides by the coefficient of x:

#x = - ((3)ln(16/25) + ln(125/64))/(ln(16/25) - ln(125/64))#

Multiply the denominator by the -1 in front:

#x = ((3)ln(16/25) + ln(125/64))/(ln(125/64) - ln(16/25))#

#x = -0.6#