# Integration rule queryWatch

#1
When you have two curves and you're told to find the area under them, how do you know which one to subtract from the other ? I was told you do the lower one subtracted from the higher one, but that didn't make any sense to me .

Eg: For this one, how do you know which side you take everything to ?

I got the answer right ,by moving everything to the left after equating, just not sure. Or does it not matter the way you do it ?
0
8 years ago
#2
it shouldn't really matter which one you subtract from the other... one way will give you a negative answer...just make it positive

the baer

1
8 years ago
#3
(Original post by WildBerry)
When you have two curves and you're told to find the area under them, how do you know which one to subtract from the other ? I was told you do the lower one subtracted from the higher one, but that didn't make any sense to me .

Eg: For this one, how do you know which side you take everything to ?

I got the answer right ,by moving everything to the left after equating, just not sure. Or does it not matter the way you do it ?
Try to imagine shapes in your head. To get that shape you need a larger shape minus a smaller shape, so you need to integrate the curve that gives the top side of the curve, minus the integral of the curve that gives the bottom side of the shape.
1
8 years ago
#4
integrating the top one gives the area under the top one

integrating the bottom one gives the area under the bottom one

you want the area between them

so top-bottom
1
8 years ago
#5
As the bear said, it doesn't matter which you take from which, it's the magnitude (absolute value) of the area that's important.

More strictly, if you want to find the area between two curves f(x) and g(x) which intersect at points x=a and x=b, you would evaluate:

The principle is the most important thing here, though.
0
#6
Thanks everyone
0
X

new posts
Latest
My Feed

### Oops, nobody has postedin the last few hours.

Why not re-start the conversation?

see more

### See more of what you like onThe Student Room

You can personalise what you see on TSR. Tell us a little about yourself to get started.

### University open days

• Cranfield University
Cranfield Forensic MSc Programme Open Day Postgraduate
Thu, 25 Apr '19
• University of the Arts London
Open day: MA Footwear and MA Fashion Artefact Postgraduate
Thu, 25 Apr '19
• Cardiff Metropolitan University
Sat, 27 Apr '19

### Poll

Join the discussion

#### Have you registered to vote?

Yes! (315)
37.77%
No - but I will (64)
7.67%
No - I don't want to (62)
7.43%
No - I can't vote (<18, not in UK, etc) (393)
47.12%