Question

ДАЮ 20 БАЛЛОВ.
хелп ми

1)7^-1 - 21^-1=
2)(0,008)^0 : (-3)^-3 =
3)(0,2cd^-3)^-2 =
​

Answer 1

$1)7^{-1}-21^{-1}=\frac{1}{7}-\frac{1}{21}=\frac{3-1}{21}=\frac{2}{21}\\\\Otvet:\boxed{\frac{2}{21}}\\\\2)(0,008)^{0}:(-3)^{-3}=1:(-\frac{1}{3})^{3}=1*(-27)=-27\\\\Otvet:\boxed{-27}\\\\3)(0,2cd^{-3})^{-2}=(\frac{1}{5}cd^{-3})^{-2}=5^{2}*c^{-2}*d^{6}=\frac{25d^{6} }{c^{2}}\\\\Otvet:\boxed{\frac{25d^{6}}{c^{2}}}$