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Question:

Evaluate: (i) sin18°cos72° (ii) tan26°cot64° (iii) cos48°−sin42° (iv) csc 31°−sec59°

Solution:

(i)sin18°cos72°=sin(90−72)°cos72°=cos72°cos72°=1
Hence, the value is 1
(ii)tan26°cot64°=tan(90−64)°cot64°=cot64°cot64°=1
Hence, the value is 1
(iii)cos48°−sin42°=cos(90−42)°−sin42°=sin42°−sin42°=0
Hence, the value is 0
(iv)csc 31°−sec59°=csc (90−59)°−sec59°=sec59°−sec59°=0
Hence, the value is 0