Area of an ellipse help? (1 Viewer)

[sean44]

Hey everybody,

Today in maths we where doing area of an ellipse. Watching the teacher explain on the board it seemed quite easy. All she did was pie multiplyed by half major axis multiplyed by half minor axis.

Simple eh?

Well then she got us to do an exercise in our textbook. And i was using tht exact formula and getting some wrong and some right. I went back over the wrong ones and did it without halving the major/minor axis and got it right.

How do i know when to half the axis or not?

Thanks heaps,
Sean

 

[PC]

Try and think about it as a circle. For a circle, the area is A = πr², and r is the radius. Sometimes you're not given the radius, but you're given the diameter, so you have to divide that by 2 to get the radius.

An ellipse is like a circle, except the radiuses are different length, so A = πab, and a and b are the two radiuses.

So before you substitute, make sure that they're the distance from centre out to the end, and not all the way across.

 

[sean44]

Try and think about it as a circle. For a circle, the area is A = πr², and r is the radius. Sometimes you're not given the radius, but you're given the diameter, so you have to divide that by 2 to get the radius.

An ellipse is like a circle, except the radiuses are different length, so A = πab, and a and b are the two radiuses.

So before you substitute, make sure that they're the distance from centre out to the end, and not all the way across.

Thanks heaps. So you saying if it runs all the way across you have to halve it. But you dont if its not all the way across?. Thanks heaps i know its frustrating to try and teach someone who dosnt understand something so thankyou for your time.

 

[khorne]

So you saying if it runs all the way across you have to halve it. But you dont if its not all the way across?.

Yes, as if it runs from one side, to the other, through the center, it is the diameter, and when you halve it, it becomes the radius.