Can We Cut Off The Sevens?

Geometry Level 2

cos ⁡ 7 ∘ , cos ⁡ 7 7 ∘ , cos ⁡ 77 7 ∘ , cos ⁡ 777 7 ∘ \large \cos7^\circ, \quad \cos77^\circ, \quad \cos777^\circ, \quad \cos7777^\circ

All of the above 4 numbers are positive except __________ \text{\_\_\_\_\_\_\_\_\_\_} .

cos ⁡ 777 7 ∘ \cos7777^\circ cos ⁡ 77 7 ∘ \cos777^\circ cos ⁡ 7 7 ∘ \cos77^\circ cos ⁡ 7 ∘ \cos7^\circ

Chung Kevin by Chung Kevin , 45, Australia

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1 solution

cos(x) is positive in the first and forth quadrant. The first three values lies on the first quadrant but cos ⁡ ( 777 7 ∘ ) \cos(7777^{\circ}) lies on the third quadrant so it is negative.

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Correct! Thank you!!

Chung Kevin - 5 years, 2 months ago

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