Answer:
centre = (- 1, - 3 ) , radius = 6
Step-by-step explanation:
the equation of a circle in standard form is
(x - h)² + (y - k)² = r²
where (h, k ) are the coordinates of the centre and r is the radius
given
x² + y² + 2x + 6y = 26 ( collect x and y terms )
x² + 2x + y² + 6y = 26
using the method of completing the square
add ( half the coefficient of the x/ y terms )² to both sides
x² + 2(1)x + 1 + y² + 2(3)y + 9 = 26 + 1 + 9
(x + 1)² + (y + 3)² = 36 ← in standard form
with centre = (- 1, - 3 ) and r = [tex]\sqrt{36}[/tex] = 6
[tex](x {}^{2} + 2x + 1) - 1 = (x + 1) {}^{2} - 1[/tex]
[tex](y {}^{2} + 6y + 9) - 9 = (y + 3) {}^{2} - 9[/tex]
[tex](x + 1) {}^{2} - 1 + (y + 3) {}^{2} - 9 = 26[/tex]
[tex](x + 1) {}^{2} + (y + 3) {}^{2} = 26 + 10[/tex]
[tex](x + 1) {}^{2} + (y + 3) {}^{2} = 36[/tex]
[tex](x - a) {}^{2} + (y - b) {}^{2} = r {}^{2} [/tex]
[tex]r {}^{2} = 36[/tex]
[tex]r = \sqrt{36} = 6[/tex]
