math
posted by marie .
If a polyhedron has 13 vertices and 21 faces, how many edges does it have?
I just need to know if I am doing this right.
v+f=e+2
13+21=34+2=36 edges.

correct.

No
v+f=e+2
e=v+f2=342=32
For a simple polyhedron F  E + V = 2. (This is also called the Euler's Formula.) 
Your equation is correct, but your answer is not. Your number of Edges is you e variable. so you are looking for the "e" what you found is "e+2"
As a general Rule with math equations, and you can do this before you put your numbers in, figure out what variable you will be looking for (in this case e=?) and move everything else to the other side of your equals sign. This will let you have an otomatic solution, because it will set you equation up as "e=..." which is exactly what you want to know, and thn you don't have the confusion that you had in this set up again.
so if your equation is v+f=e+2, e=?
then your next step is to get e alone on one side.
v+f=e+2
2= 2
v+f2=e
then plug your numbers in to get your answer.
Respond to this Question
Similar Questions

GEOMETRY
If a polyhedron has 13 vertices and 21 faces, how many edges does it have? 
Geometry
A polyhedron has 33 edges and 20 faces. How many vertices does it have? 
math
Use Eulerʹs formula to answer the question. A polyhedron has 36 edges and 21 faces. How many vertices does it have? 
math
a polyhedron has 36 edges and 21 faces, how many vertices does it have? 
math
A polyhedron has 15 vertices and 31 edges. How many faces does it have? 
Math
Use Euler’s formula to answer the question. A polyhedron has 12 edges and 6 faces, how many vertices does it have? 
Math (2 Questions)  Please Help
A cube has 8 vertices, 12 edges, and 6 square faces. A soccer ball (also known as a buckyball or truncated icosahedron) has 12 pentagonal faces and 20 hexagonal faces. How many vertices and how many edges does a soccer ball have? 
math
A polyhedron has 6 faces and 4 vertices. Use Euler's formula to calculate the number of edges. 
math
how many edges , vertices and faces does a cylinder have? 
Geometry (check)
Mario’s company makes unusually shaped imitation gemstones. One gemstone had 12 faces and 10 vertices. How many edges did the gemstone have?