Question

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

Answer 1

Answer:

r=5 units

Step-by-step 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