If A + B + C = 270°, then
cos(2A) + cos(2B) + cos(2C) is equal to :
4sin(A)sin(B)sin(C)
4cos(A)cos(B)cos(C)
1 - 4sin(A)sin(B)sin(C)
1 - 4cos(A)cos(B)cos(C)
4
3
2
1
A.
4
In a , the correct formulae among the following are
only I, II
only II, III
only I, III
I, II, III
An aeroplane flying with uniform speed horizontally one km above the ground is observed at an elevation of 60°. After 10 s if the elevation is observed to be 30°, then the speed of the plane (in km/h) is