Online Course Discussion Forum

Hi I still need some help here

 
 
YangBober的头像
Hi I still need some help here
YangBober - 2020年11月15日 Sunday 18:04
 

For 9.21 I have no idea how

For 9.23 I don't know how to find volume for this kind of triangular pyramid.

for 9.25 I don't think it's possible


Can I get some help? thanks


 
ProfessorAreteem的头像
Re: Hi I still need some help here
ProfessorAreteem - 2020年11月16日 Monday 12:37
 

9.21: Here is a diagram that might help:


This is the view obtained by cutting with a plane through the center of both spheres, and the center of the base of the cone. Since you know the radius of the bigger sphere, and the radius of the base of the cone, you can find the height of the cone. Then use similar triangles to find the radius of the smaller sphere.

9.23: The volume of any pyramid can be calculated by $V = \dfrac{A \times h}{3}$, where $A$ is the area of its base, and $h$ is its height.

9.25: Take a look at the view obtained by cutting with a vertical plane that goes through the diagonal of the square formed by the centers of the spheres of radius $1$.