Rút gọn các biểu thức sau:
a) (2x+3)^2 - 2(2x+3)(2x+5)+(2x+5)^2
b) ( x^2 +x +1)(x^2-x+1)(x^2 -1)
c) (x+y)^2 + (x-y)^2
d) 2(x-y) (x+y)+(x+y)^2+ (x-y)^2
e) (x-y+z)^2 +( z-y)^2 +2(x-y+z)(y-z)
f) (a+b-c)^2+ (a-b+c)^2 - 2(b-c)^2
g) (a+b+c)^2 +(a-b-c)^2 +(b-c-a)^2 +(c-a-b)^2
