c) 2(a – b)(a + b) + (a + b)^2 + (a – b)^2 = 4a^2;
c) 2(a – b)(a + b) + (a + b)2 + (a – b)2 = 4a2;
c) 2(a – b)(a + b) + (a + b)2 + (a – b)2
= (a + b)2 + 2(a + b)(a – b) + (a – b)2
= (a + b + a ‒ b)2 = (2a)2 = 4a2.