# Thread: its me again -.- help with another exponential question? :D

1. ## its me again -.- help with another exponential question? :D

Solve the following equation:

$\dpi{150} 2^{x+3}=2^{1-x}+15$

Answer: $\dpi{150} x=1$

I don't know what to do with the 15!!!

Thank you very much!!

2. ## Re: its me again -.- help with another exponential question? :D

Hey pumbaa213.

Apart from trial and error, you will probably have to use a root finding algorithm. Have you come across this in class?

4. ## Re: its me again -.- help with another exponential question? :D

Originally Posted by ibdutt
Do you solve the last part with logarithms or have they not been taught when solving these? I just want to make sure I am not using anything that is ''not allowed''.

5. ## Re: its me again -.- help with another exponential question? :D

You don't need logarithms. It should be obvious that if $\displaystyle 2^x= 2$ then x= 1. (You do need to know that $\displaystyle y= a^x$, for a positive, is a "one-to-one function" to know that x= 1 is the only solution.

6. ## Re: its me again -.- help with another exponential question? :D

Originally Posted by HallsofIvy
You don't need logarithms. It should be obvious that if $\displaystyle 2^x= 2$ then x= 1. (You do need to know that $\displaystyle y= a^x$, for a positive, is a "one-to-one function" to know that x= 1 is the only solution.
Okay, so we don't need logarithm until the answer becomes more complicated..Like x=2/3 or something. Right?

7. ## Re: its me again -.- help with another exponential question? :D

X is not equal to 1
2^4 is not equal to 0+15
If X = 0.9999 you get a close equality