(a-3b)²+(3a+b)²-(a+5b)²+(a-5b)²=a²-6ab+9b²+9a²+6ab²+b²-a²-10ab-25b²+a²-10ab+25b²=10a²+10b²-20ab=10(a²-2ab+b²)=10(a-b)²=10*(-8+6)²=10*4=40