Mark M. answered 06/08/24
Retired math prof. Calc 1, 2 and AP Calculus tutoring experience.
limx→0 [(secx - 1) / sinx]
Direct substitution yields the indeterminate form 0/0.
Applying L'Hopital's Rule, the given limit is equivalent to:
limx→0 [(secxtanx) / cosx)] = limx→0 [sinx / cos3x] = limx→0 [(1 / cos3x)(sinx)] = (1)(0) = 0