Answer:
Hans has done a mistake in the second step.
The correct answer is:
5x^2+13x-6=0
5x^2+15x-2x-6x=0 - 5. -6=-30 -30=15. -2
5x(1+3x)-2x(1+3x)=0
(5x-2x)(1+3x)=0
5-2x=0 1+3x=0
x=5/2 x=-1/3
