The equation for the circle below is the x2 + y2=81. what is the length of the circles radius

9

Step-by-step explanation:

Compare your x2 + y2=81 to the following:

x^2 + y^2 = 81

The " ^ " symbol indicates exponentiation.

Now compare x^2 + y^2 = 81 to

x^2 + y^2 = r^2.

This is the standard equation of a circle of radius r centered at the origin, (0,0). You can see for yourself that 81 must equal r^2.

Taking the square root of 81, we get plus or minus 9.

But the radius must be positive, so we reject the - 9 and take + 9.

The radius is 9.

Answer: 9