Tolong guys Buktikan bahwa: A. Cos x/sin^2 x-1 = -sec x B. Tan^4 x-1/sec^2 x = Tan^2 x-1

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cos x / (sin² x - 1) =  - sec x
= cos x/  -(1 - sin² x)
= cos x / -(cos²x)
= - sec x

(tan⁴ x -1) /(sec²x )  = tan²  x  -1
= (tan² +1)(tan²x -1) / sec² x
= sec² x (tan² x - 1) / sec² x
= tan² x - 1