Câu 1: 1. x.(x+y) = x2+xy
2. x4 : x2 = x2
3. x2y : xy = x
4. (x2+xy) : x
= x.(x+y) : x
= x+y
Câu 2: 1. 5x-10y=5.(x-2y)
2. x2-y2 = (x-y).(x+y)
3. x2+2xy+y2 = (x+y)2
4. x.(x-y)+2.(x-y)=(x-y).(x+2)
Câu 3: 1. 3x-9=0
=> 3.(x-3)=0
=> x-3=0
=> x=3
2. x2+2x+1=0
=> (x+1)2=0
=> x+1=0
=> x=-1