`c,E=2x^2-2x+30`
`=2(x^2-x+15)`
`=2(x^2-x+1/4+59/4)`
`=2[(x^2-2.x. 1/2+(1/2)^2)+59/4]`
`=2[(x-1/2)^2+59/4]`
`=2(x-1/2)^2+59/2`
Do `(x-1/2)^2>=0AAx`
`→2(x-1/2)^2>=0AAx`
`→2(x-1/2)^2+59/2>=59/2AAx`
`→E>=59/2`
`→E_(min)=59/2`
Dấu "=" xảy ra `↔x-1/2=0↔x=1/2`
Vậy `E_(min)=59/2↔x=1/2`