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Mathematics 11 Online
OpenStudy (johnnydicamillo):

Solve for x

OpenStudy (johnnydicamillo):

\[3^{4x} = 13 ^{-x +7}\] use base-10 logarithms

OpenStudy (zzr0ck3r):

take log of both sides \(\log_{10}(3^{4x})=\log_{10}(13^{-x+7})\\4x\log_{10}(3)=(-x+7)\log_{10}(13)\)

OpenStudy (zzr0ck3r):

you with me?

OpenStudy (johnnydicamillo):

okay I am following

OpenStudy (zzr0ck3r):

can you solve for x?

OpenStudy (zzr0ck3r):

distribute the log(13) on the right

OpenStudy (zzr0ck3r):

then add xlog(13) to both sides

OpenStudy (zzr0ck3r):

factor out the x on the left divide to get x alone

OpenStudy (zzr0ck3r):

in that order:)

OpenStudy (johnnydicamillo):

um let me try.

OpenStudy (zzr0ck3r):

k

OpenStudy (johnnydicamillo):

Okay, I am stuck on distributing logs.

OpenStudy (zzr0ck3r):

do it as you would a number

OpenStudy (zzr0ck3r):

(a+b)c = ac+bc

OpenStudy (zzr0ck3r):

here c = log(13)

OpenStudy (zzr0ck3r):

\(\log_{10}(3^{4x})=\log_{10}(13^{-x+7})\\4x\log_{10}(3)=(-x+7)\log_{10}(13)\\4x\log_{10}(3)=-x\log_{10}(13)+7\log_{10}(13)\)

OpenStudy (zzr0ck3r):

\(\log_{10}(3^{4x})=\log_{10}(13^{-x+7})\\4x\log_{10}(3)=(-x+7)\log_{10}(13)\\4x\log_{10}(3)=-x\log_{10}(13)+7\log_{10}(13)\\4x\log_{10}(3)+x\log_{10}(13)=7\log_{10}(13)\\x(4\log_{10}(3)+\log_{10}(13))=7\log_{10}(13)\\x=\frac{7\log_{10}(13)}{4\log_{10}(3)+\log_{10}(13)}\)

OpenStudy (johnnydicamillo):

okay, let me see if I understand it.

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