Question

Question 5: What is the radius of the circle with general form x2+y2-4y=21?

Question 5 options:

√21

4.58

5

25

Answer 1

r=5 units

Explanation:

we have

`x^(2)+y^(2) -4y=21`

Convert the equation of the circle in standard form

Complete the square twice. Remember to balance the equation by adding the same constants to each side

`x^(2)+(y^(2) -4y+4)=21+4`

`x^(2)+(y^(2) -4y+4)=25`

Rewrite as perfect squares

`x^(2)+(y-2)^(2)=25`

center (0,2)

radius r=5 units