find the probability

• Mar 15th 2009, 03:30 AM
szpengchao
find the probability
randomly select three positive number a,b,c, and form a triangle with sides with lengths a,b,c.

what is the probabiliy that this triangle has an angle > 90 degrees?
• Mar 15th 2009, 05:33 AM
Ruun
Hi!

I'm gonna shoot in the dark... but here are my two cents:

Supose that the triangle has an angle $\theta\ < 90$. Then you're done.

In other case the other the sum of the other angles $\theta_1+\theta_2<90$ so they can't be greather than 90.

¿Then the probability is 1? Not sure
• Mar 15th 2009, 08:43 AM
arbolis
If a=b=c then the angles are worth 60° so I'd say the probability is not worth 1. But I might be wrong since a probability of 1 doesn't mean the event will occur.
• Mar 15th 2009, 02:30 PM
awkward
Quote:

Originally Posted by szpengchao
randomly select three positive number a,b,c, and form a triangle with sides with lengths a,b,c.

what is the probabiliy that this triangle has an angle > 90 degrees?

szpengchao,

This is a poorly-stated problem and it is not possible to solve it without additional information. The reason is that you must specify some probability distribution in order to "randomly select three positive numbers a,b,c". Do you have more information about the numbers?

(There is no probability distribution which makes all positive numbers "equally likely".)