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  1. If cosec 39° = x, the value of (1 / cosec² 51°) + sin² 39°+ tan² 51° – (1 / sin² 51° sec² 39° is
    1. x² - 1
    2. 1 - x²
    3. x² – 1
    4. 1 – x²
Correct Option: C

1
+ sin²39° + tan²51° -
1
cosec²51°sin²51°.sec²39°

= sin²51° + sin²39° + tan²(90° – 39°) –
1
sin²(90° - 39°).sec²39°

[∵ sin (90° – θ) = cos θ
tan (90° – θ) = cot θ]
= 1 + cot²39° – 1
= cosec² 39° – 1 = x² - 1



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