the point with coordinates (2,-5) lies on the circumference. The center of this circumference has the coordinates (2,1). What is the radius of this circle?

The radius is

r

=

3

.

Explanation:

If the point

(

−

3

,

2

)

belongs to the circle

(

x

+

3

)

2

+

(

y

+

1

)

2

−

r

2

=

0

then its coordinates must verify that equation. That is, if we substitute in the equation of the circle

x

by

−

3

and

y

by

2

we must obtain a true equality. Then, it is enough to clear

r

of that equation:

(

−

3

+

3

)

2

+

(

2

+

1

)

2

−

r

2

=

0

⇒

9

−

r

2

=

0

,

then:

r

=

√

9

=

3

.

(Remember

r

is a distance, then it's always a positive number).

Step-by-step explanation:

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step-by-step explanation:

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