simple cos

Calculus Level 1

cos 120 = .....


The answer is -0.5.

Fauline St by Fauline ST , 23, Indonesia

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3 solutions

Prasun Biswas
Mar 13, 2014

cos ⁡ 12 0 ∘ \cos 120^{\circ}

= cos ⁡ ( 180 − 60 ) ∘ =\cos (180-60)^{\circ}

= ( − cos ⁡ 6 0 ∘ ) =(-\cos 60^{\circ}) [since cos ⁡ ( 18 0 ∘ − θ ∘ ) = ( − cos ⁡ θ ∘ ) \cos (180^{\circ}-\theta^{\circ})=(-\cos \theta^{\circ}) ]

= ( − 1 2 ) = ( − 0.5 ) =(-\frac{1}{2})=\boxed{(-0.5)}

3 Helpful 0 Interesting 0 Brilliant 0 Confused

you are great and so particular about the solutions .....nice :)

Ramandeep Kaur Arora - 7 years, 2 months ago

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Thanks for the compliment, dude !! :)

Prasun Biswas - 7 years, 2 months ago

cos(120) = cos (120 - 90)

= cos (60) = 0.5

1 Helpful 0 Interesting 0 Brilliant 0 Confused

isn't this wrong it should be -0.5

Rishabh Jain - 7 years, 3 months ago

It should be cos120=cos(180-60)=-0.5

ShubhaJyoti DEy - 7 years, 3 months ago

120 = 120-90??? non sense

Yudi Prabudi - 7 years, 1 month ago

sorry i think before i forget type - in front of 0.5

Fauline ST - 7 years, 2 months ago

Wrong

Saadat Shahidi - 7 years, 2 months ago
Kahsay Merkeb
Apr 4, 2014

c o s 120 cos120 = c o s ( 180 − 120 ) cos(180-120) = c o s ( − 60 ) = − . 5 cos(-60)=-.5

0 Helpful 0 Interesting 0 Brilliant 0 Confused

or cos(120)=cos(30+90)=cos(30) cos(90) - sin(30) sin(90)=-0.5

Claudemir Silva - 6 years, 11 months ago

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