amaths

O,A(10,5) and B(2,10) are the vertices of triangleOAB as shown in the figure.Given that C
divideds OB in the ratio 1:r and D divides OA in the ratio r:1,where r is greater than 0

http://i214.photobucket.com/albums/cc72/yesterday0721/13-1.jpg

(a)Express the coordinates of C and D in terms of r
(b)Express the area of triangleODC in terms of r
(c)If the area of triangleOAB is four times the area of triangleODC,find the value of r.