Let me know if you don’t understand anything. Hope this helped.
X² + 10x +2 = 0 .Complete the square of (x² + 10x + ??)
We know that (10x) is equal to twice the square root of the 1st (x) by ??
10x = 2.x.(??) and ?? = 5 and its square is 25. Then I have to add 25 and subtract 25 so that not to change the equation:
(x² + 10x + 25) -25 +2 =0
(x+5)² -23
I believe the answer is C.
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
