volume of a cone and a pyramid

[InterserveVB]

Can anyone explain how to do these? I have no clue even where to start

Find the volume of a right circular cone with height h = 15 and basise radius r = 7

also,

Find the volume of a pyramid with height h = 30 and rectangular base with dimesnions 3 and 6

 

[Gene]

For both of these V=a*dh.
a=the area of a a slice.
h/b = (h-y)/s
h=height
y=height of the slice
s=length of a demention of the slice at height y
For a cone s=radius and area = pi*s^2
s=b(h-y)/h
a=pi*(r(h-y)/h)² =
pi*r²(1-y/h)² =
dV=pi*r²(1-y/h)² dy
V=\(\displaystyle \int\)pi*r²(1-y/h)² dy =
pi*r²\(\displaystyle \int\)(1-2y/h+(y/h)²* dy =
pi*r²(y-y²/h+y³/(3h²)
Evaluated from y=0 to h
V=pi*r²(h - h²/h + h³/3h²)-0 =
pi*r²*h/3

The pyramid is the same replacing pi*r² with LW, the area of the base.
V=LWh/3
You should remember both from solid geometry.