Tính:

 1/. ( 2x + 3 )^2 - 2(2x+3 )( 2x + 5 ) + ( 2x + 5 )^2

2/. ( x^2 + x + 1 )( x^2 -1 + 1 )( x^2 -1 )

3/. ( a - b + c )^2 + ( a - b + c )^2 - 2(b - c )^2

4/. ( a + b + c )^2 + ( a - b - c )^2 + ( b - c - a) ^2 + ( c - a - b )^2

5/. ( x - y + z )^2 + ( z - y )^2 + 2( x - y + z )( x - y )

6/.126y^3 + ( x - 5y )( x^2 + 25y^2 + 5xy )

7/. a^3 + b^3 - ( a^2 - 2ab + b^2 )( a - b)