Question 800481
If the circle has a radius of 2 and touches the y-axis then the center is O=(a,b) where a can be 2 or -2

If a = 2 since O is on the line x + 2*y - 4 = 0 

then  2+2y-4=0 then  2y = 2 then y = 1

Then O = (2,1)



If a = -2 since O is on the line x + 2*y - 4 = 0 

then  -2+2y-4=0 then  2y = 6 then y = 3

Then O = (-2,3)

So there are 2 posible equations:

Answer:   1 circle has center O = (2,1) and radius 2

and the other circle has center O = (-2,3) and radius 2


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