Réponse:
a)soit AB^2 = a^2 + b ^2
= (a +b) × (a-b)
l 'aire de ABCD = [(a+b)×(a-b)]^2
= ( a^2 +2×a×b +b^2)×( a^2 -2×a×b+b^2 )
= (a^4 -2×a^2×b+a^2 ×b^2 + 2×a^3×b -4×a^2×b^2 +2a ×b^2 +a^2×b^2-2×a×b^2+b ^4
=a^4+b^4 - 2a^2×b -2a^2×b^2 + 2× a^3 ×b
