(cos²Ф - 1) / sin Ф 1/sin Ф=
1(cos²Ф-1) / (sin Ф sinФ)=
(cos²Ф-1) / sin² Ф=
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Fundamental relation of trigonometry:
sin²Ф + cos²Ф=1 ⇒ sin²Ф=1-cos²Ф ⇒-sin²Ф=cos²Ф-1
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-sin²Ф/sin²Ф=1
Answer: (cos²Ф - 1) / sin Ф * 1/sin Ф=-1
