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
Let "n" be a number
9 + 3n = 57
3n = 57 - 9
3n = 48
n = 48/3
n = 16
Answer:
1, 100000000
2, 100000
3, 1000000
4, 10000
Step-by-step explanation:
this Is right because you just have to keep add zero by the number of exponent
Its the last choice there. Converting that to degrees you get the interval of 90<O<120, which is the only angle that lies in the quadrant in which cosine is negative, which is the second quadrant. Cosine is also negative in the third quadrant, but you don't have choices for the third quadrant.
