(5a+6)²-4×(8+15a) a=-0,6

(5a+6)²-4×(8+15a) = 25a²+36-32-60 =
= 25a²+36-32-60 = 25a²-56
a= -0,6
25×(-0,6)²-56 = 25×0,36-56 = 9-56 = -47