`a) 3/5.(3/7)^5.(21/9)^5+(4/9)^6:(12/27)^6.`
`= 3/5.(3/7. 21/9)^5+(4/9)^6.(27/12)^6.`
`= 3/5.(3/7. 21/9)^5+(4/9. 27/12)^6.`
`= 3/5.(3/3)^5+(3/3)^6.`
`= 3/5. 1^5+1^6.`
`= 3/5. 1+1.`
`= 3/5+1.`
`= 3/5+5/5.`
`=8/5.`
`b)-63,99-(4/9-63, 99)-(-1+2/3)^2.`
`=-63,99-(4/9-63, 99)-(-3/3+2/3)^2.`
`=-63,99-(4/9-63, 99)-(-1/3)^2.`
`=-63,99-4/9+63,99-1/9.`
`=(-63,99+63, 99)+(-4/9-1/9).`
`=-5/9.`
`c) (x-2/3)^2-1=8.`
`⇒ (x-2/3)^2=8+1.`
`⇒ (x-2/3)^2=9.`
`⇒ (x-2/3)^2=(±3)^2.`
`⇒ x-2/3=3.` $\text{hoặc}$ `x-2/3=-3.`
$\text{*Trường hợp 1:}$ `x-2/3=3.`
`⇒ x=3+2/3.`
`⇒ x=9/3+2/3.`
`⇒ x=11/3.`
$\text{*Trường hợp 2:}$ `x-2/3=-3.`
`⇒ x=-3+2/3.`
`⇒ x=-9/3+2/3.`
`⇒ x=-7/3.`
$\text{Vậy x = $\dfrac{11}{3}$ hoặc x = $\dfrac{-7}{3}$.}$
`d) 3/4.(2/5)^14÷(4/25)^6.`
`= 3/4.(2/5)^14÷(2^2/5^2)^{6}.`
`= 3/4.(2/5)^14÷(2/5)^12.`
`= 3/4.(2/5)^2.`
`= 3/4. 4/25.`
`= 3/25.`
`e) (1/16)^7÷(1/8)^9`
`= (1/8.2)^7÷(1/8)^9`
`= (1^4/2^4)^7÷(1^3/2^3)^9`
`= (1/2)^28÷(1/2)^27`
`= 1/2`
