Past Paper Question (1 Viewer)

[passion89]

I'm having a bit of trouble with this question:

e^2x + 3e^x - 10 = 0


Thanks

 

[Boxxxhead]

e2x + 3ex - 10 = 0
let m = e^x
m^2 + 3m - 10 = 0.. factorises to
(m + 5)(m - 2).. then you sub e^x back in
(e^x + 5)(e^x - 2) = 0...

e^x = -5 and e^x = 2...

e^x must be > 0 so e^x = 2... convert that to log form...
therefore x = ln2

 

[passion89]

Wow it looks so easy now...thanks heaps!

 

[passion89]

I have one more question which I don't understand:

cosө= 1/(√2) for 0<ө<2pi