2條 Natural Logarithms equation

1. e^(2x+1)+ 2e^(x+2)- 3 =0
e(e^x)^2 + 2(e^2)(e^x) - 3 = 0
e^x = {- 2e^2 +/- √[4e^4 - 4e(-3)]} / 2e
e^x = - 2e^2 +/- 2√(e^4 + 3e) / 2e
e^x = 0.195940953 or - 5.63250461(rejected)
x = In 0.195940953
x = -1.6299419
2. 2e^(-2x)+ 11e^(-x)- 21 =0
2(e^-x)^2 + 11e^-x - 21 = 0
(2e^-x - 3)(e^-x + 7) = 0
e^-x = 3/2 or e^-x = - 7(rejected)
-x = In 3/2
x = - In 3/2 = -0.4054651