Do I Need A Trigonometric Table?

Geometry Level 1

cos ⁡ π 2 , cos ⁡ 2 π 3 , cos ⁡ 3 π 4 , cos ⁡ 4 π 5 \large \cos \dfrac\pi2, \quad \cos \dfrac{2\pi}3, \quad \cos\dfrac{3\pi}4, \quad \cos\dfrac{4\pi}5

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

cos ⁡ π 2 \cos\frac{\pi}2 cos ⁡ 2 π 3 \cos\frac{2\pi}3 cos ⁡ 3 π 4 \cos\frac{3\pi}4 cos ⁡ 4 π 5 \cos\frac{4\pi}5

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Chung Kevin by Chung Kevin , 45, Australia

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2 solutions

cos ⁡ ( π 2 ) = 0 \cos(\dfrac{\pi}{2})=0 and all the other three values lie on the second quadrant, where cos(x) is negative.

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You mean negative

Vishnu Bhagyanath - 5 years, 2 months ago

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Yes typo... thanks for informing

A Former Brilliant Member - 5 years, 2 months ago

Remember cos ⁡ ( θ ) , sin ⁡ ( θ ) = tan ⁡ ( θ ) \cos(\theta), \sin(\theta) = \tan(\theta) where cos ⁡ ( θ ) = x \cos(\theta) = x and sin ⁡ ( θ ) = y \sin(\theta) = y .

ADIOS!!! \LARGE \text{ADIOS!!!}

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