`y = cos x + C : y' + sin x = 0`

If y = a cos x + (b + 2x ) sin x then y _(2) + y =

y - cos y = x : (y sin y + cos y + x)y' = y

If y =a cos x + (b + 2x) sin x then show that y" + y=4 cos x.

cos x + cos y + cos z = 0 and sin x + sin y + sin z, then cos ^(2) (( x-y)/( 2)) =

I : If cos x + cos y=1/3 , sin x+sin y=1//4 " then " cos (x+y)=7//25 II : If cos x + cos y=1//3 , sin x + sin y=1//4 " then " sin(x+y)=24//25

Find the area bounded by the curves y= cos x and y= sin x between the ordinates x=0 and x= (3pi)/(2)