Question

Tìm x biết:

A)7x(x-2)-2(x-1)=21x² -14x² +3

B)3(5x-1).x(x-2)+x²-13x=7

C)\(\frac{1}{5}\)x(10x-5)-2x(x-5)=15

Answer 1

a) \(7x\left(x-2\right)-2\left(x-1\right)=21x^2-14x^2+3\)

\(\Leftrightarrow7x^2-14x-2x+2=7x^2+3\)

\(\Leftrightarrow7x^2-16x+2-7x^2-3=0\)

\(\Leftrightarrow-16x=1\)

\(\Leftrightarrow x=-\frac{1}{16}\)

b) \(3\left(5x-1\right).x\left(x-2\right)+x^2-13x=7\)

\(\Leftrightarrow\left(15x-3\right)\left(x^2-2x\right)+x^2-13x=7\)

\(\Leftrightarrow15x^3-30x^2-3x^2+6x+x^2-13x=7\)

\(\Leftrightarrow15x^3-32x^2-7x-7=0\)

Phân tích đa thức thành nhân tử, ra nghiệm vô tỉ:)

c) \(\frac{1}{5}x\left(10x-5\right)-2x\left(x-5\right)=15\)

\(\Leftrightarrow2x^2-x-2x^2+10x=15\)

\(\Leftrightarrow9x=15\)

\(\Leftrightarrow x=\frac{5}{3}\)