~ Bạn tham khảo ~
Câu 1 :
`(a+b)^2`
`= (a+b)(a+b)`
`= a^2 + ab + ab + b^2`
`= a^2 + 2ab + b^2`
`(a-b)^2`
`= (a-b)(a-b)`
`= a^2-ab-ab+b^2`
`= a^2-2ab+b^2`
Câu 2 :
`(A+B)^2=A^2+2AB+B^2`
`(A-B)^2 = A^2-2AB+B^2`
`A^2-B^2=(A-B)(A+B)`
Câu 3 :
`a, (x+5)^2=x^2+10x+25`
`b, (5x+3y)^2= 25x^2+30xy+9y^2`
`c, (x-5)^2 = x^2-10x+25`
`d, (5x-3y)^2 = 25x^2-30xy+9y^2`
`e, (x+3)(x-3)=x^2-9`
`f,(2x+3y)(2x-3y)=4x^2-9y^2`
