Prove that cos 510-cos 330-sin 390-cos 120-1

Cos 510^∘ = cos (330^∘ + 150^∘) = cos150^∘ = cos(180^∘ 30^∘) = cos 30^∘ cos 510^∘ = cos (540 30) = cos 30 cos 330^∘ = cos (360^∘ 30) = + cos 30 s ...

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Sign of Trigonometric Ratios in Different Quadrants

Prove that co...

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Prove that $c o s 510^{\circ} c o s 330^{\circ} + s i n 390^{\circ} c o s 120^{\circ} = - 1$

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cos 510^{\circ} cos 330^{\circ} + sin 390^{\circ} cos 120^{\circ} = - 1

Prove that:

$(i) t a n 720^{\circ} - c o s 270^{\circ} - s i n 150^{\circ} c o s 120^{\circ} = \frac{1}{4}$

$(i i) s i n 780^{\circ} s i n 480^{\circ} + c o s 120^{\circ} s i n 150^{\circ} = \frac{1}{2}$

$(i i i) s i n 780^{\circ} s i n 120^{\circ} + c o s 240^{\circ} s i n 390^{\circ} = \frac{1}{2}$

$(i v) s i n 600^{\circ} c o s 390^{\circ} + c o s 480^{\circ} s i n 150^{\circ} = - 1$

$(v) t a n 250^{\circ} c o t 405^{\circ} + t a n 765^{\circ} c o t 675^{\circ} = 0$

cosA + cos (120° + A) + cos(120° - A) =

cos 120^{o} = \frac{- 1}{2}

\frac{cos 135^{\circ} - cos 120^{\circ}}{cos 135^{\circ} + cos 120^{\circ}} = (3 - 2 \sqrt{2})

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