Question

12d2+34d+10=0

Answer 1

divide throughout by 2 (this is to make the coefficients smaller an easier to handle)
6d^2 + 17d + 5 = 0
6d^2 + 15d + 2d + 5 = 0
3d(2d + 5) +1(2d + 5) = 0
(3d + 1)(2d + 5) = 0
for this to be true, one of the factors has to be zero
if 3d + 1 = 0
=> 3d = -1
=> d = -1/3

if 2d + 5 = 0
=> 2d = -5
=> d = -5/2

so d= -1/3 , -5/2

Answer 2

thanks