(2x+y)^2=
= a 2 + 2ab + b 2
4x^2+4xy+y^2
( x + 4 ) 2 = x 2 + 2 ( 4 x ) + 4 2
= x 2 + 2 a x + a 2
( x + a ) 2
= x 2 + 8 x + 16
( a + b ) 2
