Bài `2:`
Ta có : `(x+2/3)^20>=0 \ AAx`
`to (x+2/3)^20 - 1/4)>=-1/4`
`to M>=-1/4`
Dấu "=" xảy ra khi : `(x+2/3)^20=0`
`<=> x=-2/3`
Vậy `M_(min)=-1/4 <=> x=-2/3`
Bài `3:`
Ta có : `(x+1)^2>=0 \ AA x`
`to -(x+1)^2<=0`
`to 4-(x+1)^2<=4`
`to E<=4`
Dấu "=" xảy ra khi : `(x+1)^2=0`
`<=> x=-1`
Vậy `E_(max)=4 <=> x=-1`
Bài `4:`
`Q=(2^27 . 9^4)/(6^9 . 8^5)`
`=(2^27 . (3^2)^4)/((2.3)^9 . (2^3)^5)`
`=(2^27 . 3^8)/(2^9 . 3^9 . 2^15)`
`=(2^27 . 3^8)/(2^24 . 3^9)`
`=(2^24 . 2^3 . 3^8)/(2^24 . 3^8 . 3)`
`=(2^3)/3=8/3`