Question 291921
let a=b^2
a^2+13a+36=0
find factors of 36 which add up to 13
1 36
2 18
3 13
4 9
6 6
(a+9)*(a+4)=0
(b^2+9)*(b^2+4)=0
b^2=-9
b^2=-4
b=2i,-2i,3i,-3i