1+(tg(a))^2= 1/(cos(a))^2
ctg(a) = 1/tg(a)
(cos(a))^2 = 1/(1+1/(ctg(a))^2) = 1/(1+1/7)=7/8
16cos²α = 16*7/8=14
1+(tg(a))^2= 1/(cos(a))^2
ctg(a) = 1/tg(a)
(cos(a))^2 = 1/(1+1/(ctg(a))^2) = 1/(1+1/7)=7/8
16cos²α = 16*7/8=14