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a)
D\ \frac{1}{x^2}=
f\left(x\right)=1{,}\ f'\left(x\right)=0\ ja\ g\left(x\right)=x^2{,}\ g'\left(x\right)=2x
\frac{0\left(x^2\right)-2x}{x^4}=\frac{-2x}{x^4}=\frac{-2}{x^3}
b)
D\ \frac{1}{x^2}=1\cdot x^{-2}=-2x^{-3}=\frac{-2}{x^{-3}}