Question

Chứng minh

a/ x² - 12x + 40 > 0

b/ -x² – 4x – 9 < 0

Answer 1

\(a,x^2-12x+40=x^2-12x+36+4=\left(x-6\right)^2+4\ge4>0\\ b,-x^2-4x-9=-\left(x^2+4x+4\right)-5=-\left(x+2\right)^2-5\le-5< 0\)

Answer 2

a/ \(=\left(x^2-12x+36\right)+4=\left(x-6\right)^2+4>0\)

b/ \(=-\left(x^2-4x+4\right)-5=-\left(x-2\right)^2-5< 0\)