Упростить cos²a+ctg²a-(1/sin²a)

cos²a+ctg²a-(1/sin²a)

cos^2(x) + ctg^2(x) - (1 + ctg^2(x)) = cos^2(x) -1

cosˇ2(a) + cosˇ2(a)/sinˇ2(a) - 1/sinˇ2(a)==cosˇ2(a)+ (cosˇ2(a)-1)/sinˇ2(a)=cosˇ2(a)- (1-cosˇ2(a))/sinˇ2(a)==cosˇ2(a)-sinˇ2(a)/sinˇ2(a)=cosˇ2(a)-1=-(1-cosˇ2(a))=-sinˇ2(a)