Question

[nguyễn hải anh]

Tìm x,biết:

a) 3x²   - 10x + 7 bé hơn hoặc bằng 0

b) 4x²  + 9x + 5 lớn hơn hoặc bằng 0

Answer 1

[ミ★kͥ-yͣeͫt★彡]

a) \(3x^2-10x+7\)

\(=3\left(x^2-\frac{10}{3}x+\frac{7}{3}\right)\)

\(=3\left(x^2-\frac{10}{3}x+\frac{25}{9}-\frac{4}{9}\right)\)

\(=3\left[\left(x-\frac{5}{3}\right)^2-\frac{4}{9}\right]\)

\(=3\left[\left(x-\frac{5}{3}\right)^2\right]-\frac{4}{3}\ge\frac{-4}{3}>0\)

Answer 2

[ミ★kͥ-yͣeͫt★彡]

b) \(4x^2+9x+5\)

\(=4x^2+9x+\frac{81}{16}-\frac{1}{16}\)

\(=\left(2x+\frac{9}{4}\right)^2-\frac{1}{16}\ge\frac{-1}{16}>0\)