1.2 has no solution. There is no number that makes

============================================

1.4

Multiply by :

The first solution will be complex and the second real

or

===========================================

1.5: e^{5x}-2e^{3x}-3e^x=0

Divide by e^x (see 1.2 as to why e^x=0 is not a solution)

Set

OR