Question

A) 4x2-7x+5=(x+2).(2x-9)

B)-x2-12x+21=(3-x).(x+11)

C)9x+5x2+1=5x2-22+13x

Lưu ý: đằng sau X có số 2 có nghĩa là _x²

Answer 1

a) \(4x^2-7x+5=\left(x+2\right)\left(2x-9\right)\)

\(\Leftrightarrow4x^2-7x+5=2x^2-5x-18\)

\(\Leftrightarrow2x^2-2x+23=0\)

\(\Rightarrow\Delta=b^2-4ac=\left(-2\right)^2-4\cdot1\cdot23=-732< 0\)

Vậy pt vô nghiệm

b) \(-x^2-12x+21=\left(3-x\right)\left(x+11\right)\)

\(\Leftrightarrow-x^2-12x+21=-x^2-8x+33\)

\(\Leftrightarrow4x+12=0\Leftrightarrow x=-3\)

c) \(9x+5x^2+1=5x^2-22+13x\)

\(\Leftrightarrow4x-23=0\Leftrightarrow x=\frac{23}{4}\)