Question

1
sin 750 degree cos 480 degree + cos 120 degreecos 60 degree equal to -1/2
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Answer 1

Answer:

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Answer 2

Answer:

sin750°cos480° + cos120°cos60°

sin(720+30)cos(360+120)+cos120cos60

sin30cos120+cos120cos60

sin30cos(90+30)+cos(90+30)cos60

sin30*(-sin30) + (-sin30)cos60

(1/2)*(-1/2)+(-1/2)(1/2)

-1/4 -1/4

= -1/2

[note: any multiple it 2π added or subtracted from an angle does not make any difference in the ratios.

hence 750 = 750-360 = 750-360*2 and so on..

further cos (90+30 ) is -sin30 as cos is negative in second quadrant and 120 is in second quadrant

[ when you shift angle by a multiple of π, sin remains sin, cos remains cos and so on. but when you shift angle by a multiple of π/2, sin becomes cos, cos becomes sin, tan becomes cot, cot becomes tan, sec becomes cosec and cosec becomes sec.]