Rút gọn biểu thức ( T = (1 + cosalpha )(1 – cosalpha ) – ta{n^2}alpha + si{n^2}alpha .ta{n^2}alpha )

Ta có:

(begin{array}{l} T = (1 – co{s^2}alpha ) – ta{n^2}alpha (1 – si{n^2}alpha ) = si{n^2}alpha – ta{n^2}.co{s^2}alpha \ = si{n^2}alpha – frac{{si{n^2}alpha }}{{co{s^2}alpha }}.co{s^2}alpha = si{n^2}alpha – si{n^2}alpha = 0 end{array})