Question

Giúp mình câu 10;11;12 nhé ạ

Answer 1

10: \(=-4x^2+2x-1\)

\(=-4\left(x^2-\dfrac{1}{2}x+\dfrac{1}{4}\right)\)

\(=-4\left(x^2-2\cdot x\cdot\dfrac{1}{4}+\dfrac{1}{16}+\dfrac{3}{16}\right)\)

\(=-4\left(x-\dfrac{1}{4}\right)^2-\dfrac{3}{4}< 0\)

11: \(=-\left(x^2-x+1\right)\)

\(=-\left(x^2-x+\dfrac{1}{4}+\dfrac{3}{4}\right)\)

\(=-\left(x-\dfrac{1}{2}\right)^2-\dfrac{3}{4}< 0\)

12: \(=-\left(x^2-3x+4\right)\)

\(=-\left(x^2-2\cdot x\cdot\dfrac{3}{2}+\dfrac{9}{4}+\dfrac{7}{4}\right)\)

\(=-\left(x-\dfrac{3}{2}\right)^2-\dfrac{7}{4}< 0\)