5ctg(a+7p/2)/4ctg(a+3p) если а=5p/4

5ctg(3π+π/2+a)/4ctga=5ctg(π/2+a)/4ctga=-5tga/4ctga=-5/4*tg²aa=5π/4-5/4*tg²(π+π/4)=-5/4*tg²π/4=-5/4*1=-1,25