Question 154450
Find an equation of the circle having center (4,-3) and radius 5?
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Plot the point (4,-3) on an x/y coordinate system. 
Draw a circle around it with radius approximately 5.
Pick any point on that circle and label it (x,y)
From that point draw a segment perpendicular to the line y=-3.
Draw a radius sement from (4,-3) to (x,y)
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You should see a right triangle with vertices at 
(4,-3), (x,y) and (x,-3)
That right triangle has hypotenuse = 5,
a side of length y+3 and a side of length x-4.
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Using Pythagoras you have:
(x-4)^2 + (y--3)^2 = 5^2
or
(x-4)^2 + (y+3) ^2 = 5^2
That is the equation for every point on th circle.
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Cheers,
Stan H.