+ Ta có:
`A=2x^2-8x-10`
`A=2(x+\frac{-8}{2.2})^2+\frac{4.2.(-10)-(-8)^2}{4.2}`
`A>=\frac{4.2.(-10)-(-8)^2}{4.2}=-18`
Dấu $"="$ xảy ra `<=>x=-\frac{-8}{2.2}=2`
Vậy $Min_A=-18$ tại `x=2`
+ Ta có:
`B=9x-3x^2`
`=-3(x^2-3x)`
`=-3(x^2-3x+\frac{9}{4})+\frac{27}{4}`
`=-3(x-\frac{3}{2})^2+\frac{27}{4}<=\frac{27}{4}`
Dấu $"="$ xảy ra `<=>x=\frac{3}{2}`
Vậy $Max_B=\dfrac{27}{4}$ tại `x=\frac{3}{2}`
+ Ta có:
`3(2^2+1)(2^4+1)(2^8+1)(2^{16}+1)`
`=(2^2-1)(2^2+1)(2^4+1)(2^8+1)(2^{16}+1)`
`=(2^4-1)(2^4+1)(2^8+1)(2^{16}+1)`
`=(2^8-1)(2^8+1)(2^{16}+1)`
`=(2^{16}-1)(2^{16}+1)`
`=2^{32}-1`
