Question

What is the value of b for the following circle in general form?

Answer 1

Answer:

the answer is indeed 4

Step-by-step explanation:

Answer 2

The equation of a circle:

$(x-h)^2+(y-k)^2=r^2$

(h, k) - center

r - radius

Look at the picture. We have

center: (1, -2) → h = 1, k = -2

radius: r = 3

Substitute:

$(x-1)^2+(y-(-2))^2=3^2\\\\(x-1)^2+(y+2)^2=9\ \ \ |\text{use}\ (a\pm b)^2=a^2\pm2ab+b^2\\\\x^2-2(x)(1)+1^2+y^2+2(y)(2)+2^2=9\\\\x^2-2x+1+y^2+4y+4=9\ \ \ |\text{use commutative property}\\\\x^2+y^2-2x+4y+5=9\ \ \ \ |-9\\\\x^2+y^2-2x+4y-4=0\\\\Answer:\ a=-2,\ b=4,\ c=-4$