1.

Find the equations of the circles whose radius is 5 and which passes through the points on X-axis at distances 3 from the origin.

Answer»

Given r = 5, passes through points on x-axis at a distance 3 from the origin 

⇒ The points are (3,0) and (-3,0) 

Let x2 + y2 + 2gx + 2fy + c = 0 is required equation (3,0)6g + C + 9 = 0 … (1) 

(-3,0) -6g + C + 9 = 0 …. (2) 

r = 5; 25 = g2 + f2 -C 

Adding 1 and 2 we get c = -9 and g = 0 and f = ±4 

∴ The required equation is x2 + y2 + 8y – 9 = 0



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