1) =74x²-74y²
2)=x²+8x+16-(x²-4)=x²+8x+16-x²+4=8x+20
3)=64a²-9b²-(36a²-60ab+25b²)=64a²-9b²-36a²+60ab-25b²=28a²-34b²+60ab
