Đáp án+Giải thích các bước giải:
`c)E=\frac{2x^2+1}{x^2+5}`
`=\frac{2x^2+10-9}{x^2+5}`
`=\frac{2(x^2+5)-9}{x^2+5}`
`=2-\frac{9}{x^2+5}`
Vì `x^2+5>=5`
`->\frac{9}{x^2+5}<=\frac{9}{x^2+5}`
`->2-\frac{9]{x^2+5}>=2-9/5=1/5`
Vậy `GTNNNN=1/5` khi `x^2+5=5<=>x=0`
`d)M=\frac{4x^2-4x+3}{(2x-1)^2+3}`
`=\frac{4x^2-4x+1+3-1}{(2x-1)^2+3}`
`=\frac{(2x-1)^2+3-1}{(2x-1)^2+3}`
`=1-\frac{1}{(2x-1)^2+3}`
Ta có: `(2x-1)^2+3>=3`
`->\frac{1}{(2x-1)^2+3}<=1/3`
`->1-\frac{1}{(2x-1)^2+3}>=1-1/3=2/3`
Vậy `GTNNNN=2/3` khi `(2x-1)^2+3=3<=>x=1/2`
