disc method across the x-axis of the graph y=-3/5x+5 bounded by both axies

Question

and how is the integral set up?

Answer 1

?????????????? "disk method" ???????????????

Answer 2

Eqn y = -3/5 + 5

From the graph,the limits are x = 0 and x = 25/3.........  

or they can be calculated alternatively by finding the x - intercept and consider the point (0,0) which is the point with the lowest x - value

V = pi ∫(5 - 3/5x)^2 dx

let u =5 - 3/5x..................du/dx = -3/5...............dx= -5/3du

By expressing the limits in terms of u

[o,25/3] = [5,0]

V = pi ∫u^2 (-5/3du)

=-5/3pi ∫u^2 du

= -5/9pi(u^3)

taking the limits [5,0]

v = 5/9pi*125

Volume = 625/9pi