x^2+y^2=81

Solution

x^{2} + y^{2} = 81

(a, b) = (0, 0), r = 9

Solution steps

x^{2} + y^{2} = 81

Rewrite

x^{2} + y^{2} = 81

in the form of the standard circle equation

(x - 0)^{2} + (y - 0)^{2} = 9^{2}

Therefore the circle properties are:

(a, b) = (0, 0), r = 9

\frac{x ^{2}}{4} + \frac{( y + 4 ) ^{2}}{25} = 1

\frac{y ^{2}}{4} - x^{2} = 1

\frac{y ^{2}}{16} - \frac{x ^{2}}{9} = 1

\frac{x ^{2}}{9} + \frac{y ^{2}}{4} = 1

\frac{x ^{2}}{9} - \frac{y ^{2}}{16} = 1