The expression for maximum height attained when the body is projected at an angle with the horizontal is :

Explanation

Time flight,
`T= (2usintheta)/g`
Average velocity
`=` (change in displcement)/Time `

Form the ure it can be said that the AB is horizontal. So there isno effect of vertical component of the velocity during this displacement.As teh body moves at a cionstant displacement, `u cos theta` in horizontal directiion, the average velocity during this displacement will be u cos theta in the horizontal direction.