4. A rocket is launched with velocity ( v ) at an angle of ( heta ) to the horizontal from the base of a hill that makes an angle of ( eta ) with the horizontal. The range of the rocket, measured along the hill's slope, is given by
( R=frac{2 v^{2} cos heta sin ( heta-eta)}{g cos ^{2} eta} ), Determine an EXACT expression for the range if ( eta=pi / 6 ). In terms of ( sin heta ) and ( cos heta ) only.(5)
