a) \(x^2+x+2=\left(x^2+x+\frac{1}{4}\right)+\frac{7}{4}=\left(x+\frac{1}{2}\right)^2+\frac{7}{4}\ge\frac{7}{4}>0\)đúng \(\forall x\in R\)
b) \(x^2-4x+10=\left(x^2-4x+4\right)+6=\left(x-2\right)^2+6\ge6>0\)đúng \(\forall x\in R\)
c) \(x\left(x-4\right)+10=x^2-4x+10\)(giải như câu b)
d) \(x\left(2-x\right)-4=-\left(x^2-2x+1\right)-3=-\left(x-1\right)^2-3\le-3< 0\)đúng \(\forall x\in R\)
e) \(x^2-5x+2017=\left(x^2-5x+\frac{25}{4}\right)+\frac{8043}{4}=\left(x-\frac{5}{2}\right)^2+\frac{8043}{4}\ge\frac{8043}{4}>0\)đúng \(\forall x\in R\)