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Grade: 10


how do you work out the perimeter of a circle which is in a larger one and a chord is given on the tangent to the smaller circle

6 years ago

Answers : (1)

ruchi yadav
askIITians Faculty
27 Points

The best way to go about a problem like this is to create a diagram of what you are actually trying to figure out. So you are starting with a circle


Then we have a circle inside of this circle and since the size of the smaller circle can change we will give this circle a radiusr.

two circles

Now the toughest part is placing the chord. It says that the chord rests on top of the smaller circle so we can place it anywhere.

with chord

A theorem in geometry is that if a chord touches the edge of a circle it creates a right angle with the radius of that circle.

and additional radius

Then from here we can use the Pythagorean Theorem to help us find the radius of the big circle. Since the length of the chord is x half of that would be 50 and this would be one of the legs of the right triangle, then the radiusrwould be the length of the other leg of the right triangle. So your equation for the radius R of the larger circle can be figured out using the Pythagorean Theorem and looks like the following equation R2= r2+x2. Thus i you know the radius r of the smaller circle you can find the radius R of the larger circles radius you then can use A=pR2o find the area of the larger circle.

Hope this helps.

Thank You


Askiitians Faculty

6 years ago
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