Question

Помогите пожалуйста решить! :)

Answer 1

$\displaystyle\bf\\1) \ \ b^{2}-8b+15=0\\\\D=(-8)^{2}-4\cdot15=64-60=4=2^{2} \\\\\\b_{1} =\frac{8-2}{2} =\frac{6}{2} =3\\\\\\b_{2} =\frac{8+2}{2} =\frac{10}{2} =5\\\\\\b^{2} -8b+15=(b-3)(b-5)\\\\\\2) \ \ b^{2}-25=b^{2} -5^{2} =(b-5)(b+5)\\\\\\\\3) \ \ \frac{b^{2} -8b+15}{b^{2} -25} =\frac{(b-3)(b-5)}{(b-5)(b+5)} =\frac{b-3}{b+5} \\\\\\Otvet \ : \ \frac{b^{2} -8b+15}{b^{2} -25} =\frac{b-3}{b+5}$