求積法。急！！！！！?

Projectional view = Trapezoid ABGF

Vertex = O = (0,0)

Plot OJ⊥AB & OK⊥GF

ΔOGF: OJ / (OJ + 12) = 20 / 30 = 2/3

OJ / 12 = 2 / 1

=> OJ = 24 cm

=> B = (10,24)

=> Line OBG: y = 12x/5

=> dy = 12/5 * dx

=> dV = (2x)^2*dy = 48/5 * x^2 * dx



V = ∫(2x)^2*dy

= 4∫x^2*12/5 * dx

= 48/5 * x^3/3 ;;; x = 10~15

= 16/5 * (15^3 - 10^3)

= 16/5 * (3375 - 1000)

= 16*2375/5

= 16*475

= 7600 cm^3