Can you help me find the answer?

e^(4x) + 4e^(2x) - 21 = 0

1 Answer
Apr 13, 2017

x=1.0986

Explanation:

In e^(4x) + 4e^(2x) - 21 = 0, let e^(2x)=u

then the equation becomes

u^2+4u-21=0

or u^2+7u-3u-21=0

or u(u+7)-3(u+7)=0

or (u-3)(u+7)=0

bur as u=e^x, u+7!=0 and dividing by u+7, we get

u-3=0 or e^x=3 i.e. x=ln3=1.0986