Solve the simultaneous equations and .

I have tried substituting into and also changing into . I seem to be going on and on without really going anywhere with my working.

Could really do with some help. Thanks

Printable View

- Jul 5th 2009, 01:47 AMgreghunterlogarithms help
Solve the simultaneous equations and .

I have tried substituting into and also changing into . I seem to be going on and on without really going anywhere with my working.

Could really do with some help. Thanks - Jul 5th 2009, 01:57 AMCaptainBlack
- Jul 5th 2009, 02:01 AMProve It
- Jul 5th 2009, 09:26 AMgreghunter
Thanks, I didn't realise you could stick a log infront but it does make sense

- Jul 5th 2009, 05:57 PMblockfrom3062

Divide the second equation by the first giving 2 = (7^y)/(5^y)

then 2 = (7/5)^y or 2 = (1.4)^y

Solve for y = ln 2 / ln 1.4

Substitute into the first equation for y

4^(x) = 5 ^(ln 2/ ln 1.4)

x ln 4 = (ln2/ln1.4) (ln 5); change ln 4 to ln 2^2 = 2 ln 2

x = (ln 1.4) (ln 5)/(ln 2)