Question

(7b-3)*(7b+3)-7b*(7b+3) при b= -2,5

Answer 1

$(7b-3)*(7b+3)-7b(7b+3)=49b^{2}-9-49b^{2}-21b=-9-21b$

При $b=-2,5$

$-9-21*(-2,5)=-9+52,5=43,5$