ĐK : \(y\ne2x,a\ne-b\)
\(A=\frac{ac+bx+ax+bc}{ay+2bx+2ax+by}\)
\(=\frac{\left(ac+ax\right)+\left(bx+bc\right)}{\left(ay+by\right)+\left(2ax+2bx\right)}\)
\(=\frac{a\left(c+x\right)+b\left(c+x\right)}{y\left(a+b\right)+2x\left(a+b\right)}\)
\(=\frac{\left(c+x\right)\left(a+b\right)}{\left(a+b\right)\left(y+2x\right)}\)
\(=\frac{c+x}{y+2x}\) không phụ thuộc vào \(a,b\) ( đpcm )