а)а-(1/а)=2/3⇒а²+(1/а²)-2а/а=4/9⇒а²+(1/а²)=2 4/9=22/9
б) а³-(1/а³)=(а-(1/а))(а²+1+(1/а²))=(2/3)*(1+2 4/9)=2*31/(3*9)=62/27=2 8/27
в)(а¹²+1)/а⁶=а⁶+(1/а⁶)=(а²)³+(1/а²)³=(а²+(1/а²))*(а⁴+(1/а⁴)-1)=
(22/9)*((а²+(1/а²))²-3)=22/9*((22/9)²-3)=22*(484-243)/(81*9)=22*241/729=
5302/729=7 199/729