area uner an exponential

[jadzia49]

what is the area under y=e^-x from o to infinity

[jadzia49]

just found the answer thanks.answer is 1

[fo3nix]

-1.

You just integrate it.

[factor-fiction]

Just trying to remember my O level maths.
I think integral of e^-x is -(e^-x).
So area = [-e^0]] - [-e^-∞]
= -1 - 0
=-1

But can area be -1.

Think it must be 1

[fo3nix]

Yea, exactly.

Area is a positive quantity.

[jadzia49]

should be 0- (-1)=1

[gravitate]

man i did a degree in engineering 2 year and i havent got a clue as i 4gotton everything. What u need to know for? Is maths a hobby for u?

[derrynoose]

When substituting limits in definite Integration, the higher limit is substituted first, then the lower limit.This will give the area as +1in this case.
A negative outcome to the calculation of an area by definite integration is an indication of the location of the area i.e. below the axis if the integration is with respect to x.

[fo3nix]

Yea, above is totally correct.

I have no idea how I came to writing it as -1.