Question

Tìm x,y biết:

a) \(-2x\left(10x-3\right)+5x\left(4x+1\right)=25\)

b) \(y\left(5-2y\right)+2y\left(y-1\right)=15\)

c) \(x\left(x+1\right)-\left(x+1\right)=35\)

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

Answer 1

a) \(-2x\left(10x-3\right)+5x\left(4x+1\right)=25\)

\(-20x^2+6x+20x^2+5x=25\)

\(\Rightarrow6x+5x=25\)

\(\Rightarrow11x=25\)

\(\Rightarrow x=\dfrac{25}{11}\)

b) \(y\left(5-2y\right)+2y\left(y-1\right)=15\)

\(5y-2y^2+2y^2-2y=15\)

\(\Rightarrow5y-2y=15\)

\(\Rightarrow3y=15\)

\(\Rightarrow y=5\)

c)\(x\left(x+1\right)-\left(x+1\right)=35\)

\(\Rightarrow\left(x-1\right)\left(x+1\right)=35\)

\(\Rightarrow x^2-1=35\)

\(\Rightarrow x^2=36\)

\(\Rightarrow x=6;x=-6\)

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

\(x^3+x^2+x-x^3+x=0\)

\(\Rightarrow x^2+2x=0\)

\(\Rightarrow x\left(x+2\right)=0\)

\(\Rightarrow x=0;x=0-2=-2\)

Vậy \(x=0;x=-2\)