Question

i want the formula of area of kite and its derivation
  

Answer 1

divide the kite into 2 triangles by drawing a line from the 2 opposite corners that are closer than the other 2 opposite corners. the 2 triangles have the same base, so the area of each is 1/2bh and 1/2bH. total area is 1/2b(h+H), which is the same as 1/2 the area of a rectangle with height and width the lengths of the distances between the opposite corners of the kite. ............... So area of kite = 1/2 product of diagonals