notice the picture below
due to equal sides on each scalene triangle, the angle bisector cuts the horizontal in half
thus, use the pythagorean theorem to get the "b" or opposite side
[tex]\bf c^2=a^2+b^2\implies \sqrt{c^2-a^2}=b[/tex]
also notice, that "b" is also the altitude or height "h"
what's the area? well, area of a triangle is 1/2 bh
get the area of each triangle and sum them up, that's the area of the kite