Posted by **Jessie** on Friday, December 20, 2013 at 7:06pm.

If (x, y) is on the graph f(x) = log(base10)x, state the coordinates (in terms of x and y) that would be on the graph of f(x) = 2log(base10)(x - 4) + 3?

Can you please explain how to answer this question? Thanks!

- Advanced Functions/ Precalculus Log -
**Reiny**, Friday, December 20, 2013 at 9:18pm
remember if the base of the log is 10, we don't have to write the base.

so you have y= logx

and y = 2log(x-4)+3

intersection:

2log(x-4) + 3 = logx

log(x-4)^2 - logx = -3

log ( (x-4)^2 /x ) = -3

(x-4)^2 /x = 10^-3

x^2 - 8x + 16 = (1/1000)x

1000x^2 - 8001x + 16000=0

using the formula

x = (8001 ± 126.5)/2000

= 4.06 or 3.94

but in 2log(x-4) , x-4> 0 , so our 2nd answer is rejected

x = appr 4.06

if x = 4.06, then y = log 4.06 = appr .61

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