5X+12Y=0
y=-5/12x
tanα=k=-5/12
X小于等于0,∴α在第二象限
cosα=-1/根号(1+tan^2α)=-1/根号(1+5^2/12^2)=-12/13
sinα=根号(1-cos^2α)=根号(1-12^2/13^2)=5/13
cosα+1/tanα-1/sinα
=-12/13+1/(-5/12)-1/(5/13)
=-12/13-12/5-13/5
=-12/13-5
=-77/13