1、(5x-3y-2xy)-(6x+5y-2xy)
=5x-3y-2xy-6x-5y+2xy
=-x-8y
将x=-5,y=-1代入得 -（-5）-8（-1）=5+8=13
2、【50-（7/9-11/12+1/6）×（-6）^2】÷（-7）^2
=[50-(28/36-33/36+6/36)×36]÷49
=[50-1/36×36]÷49
=(50-1)÷49
=49÷49
=1