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Find the value of 8 cos 10° cos20° cos 40°.
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- tan80°
- cot10°
- tan80° or cot 10°
- None of these
- tan80°
Correct Option: C
Expression = 8 cos 10°. cos 20° . cos 40°
| Expression = 4 |  |  | ||
| sin 10° |
| Expression = 2 | | | ||
| sin 10° |
{ ∴ 2 sinθ . cosθ = sin2θ }
| Expression = | | | ||
| sin 10° |
| Expression = | = | ||
| sin 10° | cos (90° - 10°) |
| Expression = | or | ||
| cos 80° | sin 10° |
Expression = tan80° or cot 10°
{ ∴ cos (90° - θ) = sinθ and sin (90° - θ) = cosθ }
