69,420,911,80085 and that’s all
18=1,2,3,9,18
37=1,37
48=1,2,3,16,24,12,4,6,8,48
Prime no. is a number that is divisible only by itself and 1
So, here 37 is a prime no.
18 and 48 are composite no.s
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
