1, ( x + 2y )^2 = x^2 + 4xy + 4y^2
2, ( 2x + 3y )^2= 4x^2 + 12xy + 9y^2
3, ( 3x - 2y )^2 = 9x^2 - 12xy + 4y^2
4, ( 5x - y )^2 = 25x^2 - 10xy + y^2
5, ( x + 1/4 )^2 = x^2 + 1/2x + 1/16
6, ( 2x - 1/2 )^2 = 4x^2 - 2x + 1/4
7, ( 1/3 x - 1/2y )^2 = 1/9.x^2 - 1/3xy + 1/4y^2
8, ( 3x + 1 ) ( 3x - 1 ) = 9x^2 -1
9, ( x^2 + 2/5y ) ( x^2 - 2/5y ) = x^4 - 4/25y^2
10, (x/2 - y ) ( x/2 + y ) = x^2/4 - y^2
11, (  x/2 - 2y )^2 = x^2/4 - 2xy + 4y^2
12, ( 2x - y )^2 = 4x^2 - 4xy + y^2
13, ( 3/2x + 3y )^2 = 9/4x^2 + 9xy + 9y^2
14, ( 2x + 8y )^2 = 4x^2 + 32xy + 64y^2
15, ( x + 1/6y + 3 )^2 = x^2 + 1/36y^ + 9 + 1/3xy + y + 6x
16, ( 1/2 x - 4y )^2 =  1/4x^2 - 4xy + 16y^2
17, ( x/2 + 2y^2 ) ( x/2 - 2y^2 ) = ( x^2 )/4 - 4y^4
18. ( x^2 - 4 ) ( x^2 + 4 ) = x^4 - 16
19. ( x + y )^2 + ( x - y ) ^2 = x^2 + 2xy + y^2 + x^2 - 2xy + y^2 = 2 . ( x^2 + y^2 )