What should be the angle of projection with horizontal for a body to attain maximum height for a given velocity of projection?

A particle of mass m is projected with an initial velocity u at an angle theta to horizontal. The torque of gravity on projectile at maximum height about the point of projection is

The path of a projectile is given by the equation y = ax – bx^(2) , where a and b are constants and x and y are respectively horizontal and vertical distances of projectile from the point of projection. The maximum height attained by the projectile and the angle of projection are respectively.