Question

a,x^2.(x-1)-4x^2+8x-4=0 (tìm x)

b,x.(x+2)-(x-3).(x+3)=7.(x-1)

c,5x^2-15=7x-21

Answer 1

a: \(\Leftrightarrow x^2\left(x-1\right)-4\left(x-1\right)^2=0\)

\(\Leftrightarrow\left(x-1\right)\left(x^2-4x+4\right)=0\)

\(\Leftrightarrow\left(x-1\right)\left(x-2\right)^2=0\)

=>x=1 hoặc x=2

b: \(\Leftrightarrow x^2+2x-x^2+9=7x-7\)

=>2x+9=7x-7

=>-5x=-16

hay x=16/5

c: \(5x^2-15=7x-21\)

\(\Leftrightarrow5x^2-7x+6=0\)

\(\text{Δ}=\left(-7\right)^2-4\cdot5\cdot6=49-120=-71< 0\)

Do đó: Phương trình vô nghiệm