9x^2 + 9y^2 = 63

Question

You have to find the radius of the circle

Answer 1

The general form of a circle is:

 

x² + y² = r², where are is the radius.

 

So just copy the form, from:

 

9x² + 9y² = 63, notice in the form that the x and y shouldn't have any coefficients. So divide both sides by 9.

 

x² + y² = 7. From here this is the part that most students commit mistake, they will answer that the radius is 7.

 

Wrong. Observing the form again, that part in the equation is r².

 

Meaning r² = 7,

 

So the correct r = √7