answer: r=4
explanation:
1. subtract 9 from both sides to get the constant to the right
2. use the commutative property to reorder the terms so that 10x is in the middle of x^2 and y^2
3. to complete the square, a same value needs to be added to both sides:
x^2 + 10x + ? + y^2 = -9 + ?
4. to complete the square, add 25 to the expression:
x^2 + 10x + 25 + y^2 = -9 + 25
5. use formula a^2 + 2ab + b^2 = (a+b)^2 to factor the expression
(x+5)^2 + y^2 = -9 + 25
6. rewrite/calculate:
(x+5)^2 + y^2 = 16
7. then write in the circle formula to find radius r=4 and center (-5,0)
Hope this helps :)
