# how to solve this exponential equation?

• Apr 27th 2012, 11:39 AM
kukid13
how to solve this exponential equation?
whats solution to (3)^2x-36(3)^x+243=0
• Apr 27th 2012, 11:49 AM
a tutor
Re: how to solve this exponential equation?
\$\displaystyle (3^x)^2-36(3^x)+243=0\$

Substitute \$\displaystyle y=3^x\$ if you like. Factorise.
• Apr 27th 2012, 11:51 AM
kukid13
Re: how to solve this exponential equation?
then you just use quadratic formula?
• Apr 27th 2012, 11:54 AM
a tutor
Re: how to solve this exponential equation?
That will certainly work.
• Apr 27th 2012, 12:01 PM
kukid13
Re: how to solve this exponential equation?
your solution set is 9, -27, but when i try testing them with original equation im not getting right answer, is there something im missing
• Apr 27th 2012, 12:34 PM
skeeter
Re: how to solve this exponential equation?
Quote:

Originally Posted by kukid13
your solution set is 9, -27, but when i try testing them with original equation im not getting right answer, is there something im missing

you should have found 9 and +27 for your quadratic solutions ..
• Apr 27th 2012, 12:45 PM
kukid13
Re: how to solve this exponential equation?
but when i try to plug those back into equation im coming up with funky answers? what am i missing
• Apr 27th 2012, 12:50 PM
skeeter
Re: how to solve this exponential equation?
Quote:

Originally Posted by kukid13
but when i try to plug those back into equation im coming up with funky answers? what am i missing

\$\displaystyle 3^x = 9\$

\$\displaystyle x = 2\$

you do the other solution ...