a)2(x - y)(x + y) + (x + y)²+ (x - y)²

=2.x²-y² +x²+2xy+y²+x²-2xy+y²

=(2x²+x²+x²)+(-y²+y²+y²)+(2xy-2xy)

=4x²+y²

b)(x - y + z)²+ (z - y)²+ 2(x - y + z)(y - z)

=x²-y²+z²+z²-2zy+y²+2x-2y²+2z²

=(-y²+y²-2y² ) +(z²+z²+2z²) +x²-2zy+2x

=-2y² +4z²+x²-2xy +2x

( 3x - 1 ) ( 2x + 7 ) - ( x + 1 ) ( 6x - 5 ) - x - 2 + ( x + 5)

=6x²+21x-2x-7-6x²+5x-6x+5-x-2+x+5

=(6x²-6x²)+(21x-2x+5x-6x-x+x)+(-7+5+5-2)

=18x-1