Question

i need do demonstrate sin 5+ sin 125+sin245=0

Answer 1

Use \[ \sin(x+y)=\sin(x)\cos(y)+\cos(x)\sin(y) \] once with with x=5 and y=120 and then with x=5 and y=240. Then add together the terms.

Answer 2

Or think of it as points lying on the unit circle.

Answer 3

sin5 + sin (120 + 5 ) + sin (240 +5 )

Answer 4

sin5 + sin120cos5 +cos120sin5 +sin240cos5+cos240sin5

Answer 5

And then use known values of sin and cos.

Answer 6

thx