(MX+NY)²+(NX-MY)²
=M²X²+2MNXY+N²Y²+N²X²-2MNXY+M²Y²
=M²X²+N²Y²+N²X²+M²Y²
=M²(X²+Y²)+N²(X²+Y²)
=(M²+N²)(X²+Y²)
=5*41
=205