# Math question... I need help!

Asked by silverangel (936) October 15th, 2011

It’s a logarithm question, it says: “Solve the equation 5 power 2x + 7(5 power x) -30 =0
PS: it’s not a HW question and I already know the answer, it’s just that I need someone to explain the steps

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Post the answer to show that you know it.

ratboy (15142)

Do you mean this?

CWOTUS (24134)
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[mod says] Please do not provide the actual answer to the problem. Only help in solving it. Thanks!

augustlan (47243)

@augustlan okay. I thought I can, since it’s not a home work.

Here, again, just the first trick and links to follow.
5^2x + 7*(5^x) – 30 = 0
Rearranging.

[(5^x)^2] + 7*(5^x) – 30 = 0

Now, the trick is, put y = 5^x,
y^2 + 7*y – 30 = 0

From this on, solve the quadratic equation, get two values of y. Test the values. Apply logarithms, and solve to get the answer.
For logarithms, you may refer:
Basics of logarithms
Log rules
Simplifying logarithms (6th bullet point)
Changing base of log

Response moderated (Writing Standards)