Question

Answer 1

1) \(\left(2x+3y\right)^2\)

\(=\left(2x\right)^2+2\cdot2x\cdot3y+\left(3y\right)^2\)

\(=4x^2+12xy+9y^2\)

2) \(\left(5x-y\right)^2\)

\(=\left(5x\right)^2-2\cdot5x\cdot y+y^2\)

\(=25x^2-10xy+y^2\)

Answer 2

`@` `\text {Ans}`

`\downarrow`

`1)`

`(2x + 3y)^2`

`= (2x+3y)(2x + 3y)`

`= 2x(2x + 3y) + 3y(2x + 3y)

`= 4x^2 + 6xy + 6xy + 9y^2`

`= 4x^2 + 12xy + 9y^2`

`2)`

`(5x - y)^2`

`= (5x-y)(5x-y)`

`= 5x(5x - y) - y(5x - y)`

`= 25x^2 - 5xy - 5xy + y^2`

`= 25x^2 - 10xy + y^2`

____

`@` CT (nếu đang học hè lớp 7 `->` 8)

`(A+B)^2 = A^2 + 2AB + B^2`

`(A - B)^2 = A^2 - 2AB + B^2`