# Thread: 2D probability integral question..

1. ## 2D probability integral question..

the question and solution
after i they find the total interval of the total function
i cant understand
what they do with the graph and how they derive the integrals from it
?

2. It looked like a minus sign, but this a product.
You want to find the area under xy=k where 0<k<1.
Your instructor looked at the complement, which is easier, since you only need one region instead of two.

3. i cant understand this graph
i understand the x1 and x2 are from 0 to 1 so we get a square
but from where comes this curve?

why we want " to find the area under xy=k where 0<k<1."

4. it is called an hyperbola, let k=.5
xy=.5 is y=.5/x.

5. how do we know what area to calculate?

6. As it states in your notes, it's xy<k. This is basic calc 3.

7. how to we know that x1x2<t is bellow this line
how to we know that x1x2>t is above this line

8. Originally Posted by transgalactic
how to we know that x1x2<t is bellow this line
how to we know that x1x2>t is above this line
it is a curve not a line
pick a POINT, try (0,0)

9. if we take the curve y=1/x
how to know that (0,0) is beloow y=1/x
?

10. Originally Posted by transgalactic
if we take the curve y=1/x
how to know that (0,0) is beloow y=1/x
?
draw xy=1, BUT isn't (0)(0)=0<1?

11. thanks