Question

How do you find the equation of the circle given center at (1,-3), and radius 10?

Answer 1

Answer:

note: all the twos are to the power

100=(x−1)2(y+3)

Step-by-step explanation:

Suppose the centre of the circle was at the origin (where the x axis crosses the y axis). Then the equation would be:

r2=x2+y2

The reason for this format is that the length of the radius (which is of fixed length) can be related to x and y by Pythagoras. However, the circle centre is not at the origin. It is at

(x,y)→(1,−3)

So we can mathematically make this work by 'theoretically' moving the actual centre to a new centre located at the origin.

Thus we would have:

r2=(x−1)2+(y−(−3))2

r2=(x−1)2+(y+3)2

But the radius is 10 so we have

(10)2=(x−1)2+(y+3)2

100=(x−1)2+(y+3