lim(x→0)[(secx)^2-1] /(1-cosx)

lim(x→0)[(secx)^2-1] /(1-cosx)

lim(x→0)[(secx)^2-1] /(1-cosx)
=lim tan²x/[(1/2)x²]
=lim x²/[(1/2)x²]
=1/2