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)
In a , the correct formulae among the following are
only I, II
only II, III
only I, III
I, II, III
C.
only I, III
Therefore I and III statements are true but II is a false statement.
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