So the question is: A curve rise from the origin of the xy plane into the 1st quadrant. The area under the curve from (0,0) to (x,y) is 1/5 the area of the rectangle with these points as opposite vertices. So i'm solving for f(x): So far what i have is: Area(D)=1/5 xy=integral 0 to x y(t)dt and then...