1、(3x-5)*(3x-5)-(2x+7)*(2x+7)
=(9x*x+25-30x)-(4x*x+49+28x)
=5x*x-2x=74
2、(x+y+1)(x+y-1)
=(x+y)*(x+y)—1*1
=x*x+y*y+2xy-1