Question : The value of $(1+\sec20°+\cot70°)(1-\operatorname{cosec}20°+\tan70°)$ is equal to:
Option 1: 0
Option 2: 1
Option 3: 2
Option 4: –1
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Correct Answer: 2
Solution :
Given: $(1+\sec20°+\cot70°)(1 – \operatorname{cosec}20°+\tan70°)$
= $(1+\sec20°+\tan20°)(1-\operatorname{cosec}20°+\cot20°)$
= $(1+\frac{1}{\cos20°}+\frac{\sin20°}{\cos20°})(1–\frac{1}{\sin20°}+\frac{\cos20°}{\sin20°})$
= $(\frac{\cos20°+1+\sin20°}{\cos20°})(\frac{\sin20°–1+\cos20°}{\sin20°})$
= $\frac{(\sin20°+\cos20°)^{2}–1^{2}}{\cos20°\sin20°}$
= $\frac{\sin^{2}20°+\cos^{2}20°+2\sin20°\cos20°–1}{\cos20°\sin20°}$
= $\frac{2\sin20°\cos20°}{\cos20°\sin20°}$
= $2$
Hence, the correct answer is 2.
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