Question

№4. Упростите выражение и найдите его значение:
1)(а-7х)/а:(ах-7х^2)/а^2 при а = 3, х = -9 ,
2) (3ас^2)/(а^2-16с^2 )⋅(а-4с)/ас при а=2,1 с=-0,4,
3) (8в – 8)(8в + 8) – 8в(8в + 8) при в = 1,6

Answer 1

$\frac{a-7x}{a}: \frac{ax-7x^2}{a^2}= \frac{a-7x}{a}* \frac{a^2}{ax-7x^2}=\frac{a-7x}{a}* \frac{a^2}{x(a-7x)}= \frac{a}{x} \\ \frac{a}{x}=\frac{3}{-9}=- \frac{1}{3} \\ \\ \frac{3ac^2}{a^2-16c^2}* \frac{a-4c}{ac}=\frac{3ac^2}{(a-4c)(a+4c)}* \frac{a-4c}{ac}= \frac{3c}{a+4c} \\ \frac{3c}{a+4c}=\frac{3*(-0.4)}{2.1+4(-0.4)}= \frac{-1.2}{2.1-1.6}= -\frac{1.2}{0.5}=-1.2*2=-2.4 \\ \\ (8b-8)(8b+8)-8b(8b+8)=(8b)^2-8^2-64b^2-64b= \\ =64b^2-64-64b^2-64b=-64-64b=-64(1+b) \\ -64(1+b)=-64(1+1.6)=-64*2.6=-166.4$