Buktikan tan x sin x + cos x = 1/cosx!

tanx sinx + cosx = 1/cosx

* ingat tanx = sinx/cosx

= (sinx/cosx) . sinx + cosx
= sin²x/cosx + cosx

(samakan penyebutnya)

= sin²x/cosx + cos²x/cosx
= (sin²x+cos²x)/cosx

*ingat sin²x+cos²x = 1

= 1/cosx (terbukti)