Question

Revised: I forgot a part: f(x)=5(3)^x Find x when f(x)=105

Answer 1

105 = 5(3)^x

Answer 2

21 = 3^x

Answer 3

lo take log on both sides to solve

Answer 4

Yes, and x = 2.77

Answer 5

Hero - How did you get the 2nd step of 21=3^x?

Answer 6

I divided both sides by 5

Answer 7

Oh!! That makes sense! Thanks!

Answer 8

What about the 3rd part..how did you get your answer of 2.77?

Answer 9

I took logs of both sides....

Answer 10

When I did that, I got:

log (21) = x log (3)

Answer 11

ln(21) = ln(3^x)
ln(21) = x ln(3)
x = ln(21)/ln(3)

Answer 12

Then I divided both sides by log (3):

\[\frac {\log (21)} {\log (3)} = x\]

Answer 13

2.77 = x

Answer 14

Got it! Thanks!

Answer 15

approximately