Câu 1 :
\(a,\left(x-2\right)\left(x+5\right)=x^2+5x-2x-10=x^2+3x-10\)
b, Sửa đề : ( mk ko bt đề bn ntn , có 2 TH sửa ,mk lm cả 2 ,cái nào đg thì bn xem nhé )
C1 : \(3x-3y+ax-ay\)
\(=3\left(x-y\right)+a\left(x-y\right)\)
\(=\left(x-y\right)\left(a+3\right)\)
\(C_2:3x+3y+ax+ay\)
\(=3\left(x+y\right)+a\left(x+y\right)\)
\(\left(x+y\right)\left(a+3\right)\)
\(c,\left(x^2+2xy\right):\left(x+2y\right)\)
\(=x\left(x+2y\right):\left(x+2y\right)\)
\(=x\)
\(d,\left(x-2\right)\left(x+2\right)+\left(x+1\right)^2-2x^2=0\)
\(\Rightarrow x^2-4+x^2+2x+1-2x^2=0\)
\(\Rightarrow2x-3=0\)
\(\Rightarrow x=\dfrac{3}{2}\)