Answer:
it is D
Step-by-step explanation:
I know things dude. I got your back :-)
Answer:
This would be a regular polygon.
Step-by-step explanation:
A regular polygon has congruent sides and interior angles.
An irregular polygon does not have congruent sides and all interior angles.
A convex polygon does not have a interior angle greater than 180°.
Lastly, a concave polygon has only one interior angle greater than 180°.
Using the process of elimination, it would not be a convex or concave polygon. Now we have either a regular or irregular polygon. This polygon can not be a irregular polygon because all the sides are congruent. This means that this polygon is a regular polygon!
We know, cos A + cos B = 2cos(C+D)/2 × cos(C - D)/2
So,
cos 130 + cos 110 + cos 10
cos 130 + 2cos (110+10)/2 × cos( 110-10)/2
cos 130 + 2cos 60 × cos 50
cos ( 180 - 50 ) + 2cos60 cos 50
We know, cos ( 180 - A ) = -cos A
2cos 60 cos 50 - cos 50
Also, cos 60 = 0.5
2×0.5 cos 50 - cos50
cos 50 - cos 50
0 = RHS.
Hence proved
