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May 22, 2023
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A circle is centered at the origin and has a radius of square root 130. Work out the coordinates of the two points on the circle where x=7  

 

The first answer made a mistake.  

Used 130 for r instead of sqrt(130).  

The numbers got really big after that.  

 

The equation of a circle centered at the origin is x2 + y2 = r2   

 

We already know the x coordinate is 7, because the problem tells us that, 

so we only have to solve for y.  So plug the 7 in for x and sqrt(130) in for r  

into the equation.  

 

                                                                       x2 + y2  =  r2   

 

                                                                       72 + y2  =  [sqrt(130)]2  

 

                                                                       49 + y2  =  130  

 

                                                                               y2  =  130 – 49  

 

                                                                               y2  =  81  

 

                                                                               y   =  +9  

 

So the coordinates are                                  (7, 9) and (7, –9)  

.

May 22, 2023

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