Question

Sin780sin480 +cos120cos60=0.5
Prove the above without using the trigonometry table.

Answer 1

well sin 780 = sin(60)
sin480 = sin(60)

cos(120) = - cos(60)

using exact values it



\[\frac{\sqrt{3}}{2}\times \frac{\sqrt{3}}{2} + \frac{-1}{2} \times \frac{1}{2}\]

now just simplify

Answer 2

Ya bug the problem specifies that solve without using trigonometric values.......

Answer 3

it says without using tables... the values shown are exact values... and are known by most students who study trig.

Answer 4

I assumed that the table meant the normal trigonometric table....... That shows the exact value.... Got it cleared.... Thank you..... :) :)