A=(4;1), B=(1,5)
d=|AB|=\sqrt{(x_B-x_A)^2+(y_B-y_A)^2}=\sqrt{(1-4)^2+(5-1)^2}=\sqrt{(-3)^2+4^2}=\sqrt{9+16}=\sqrt{25}=5
r=\frac{1}{2}d=\frac{1}{2}*5=\frac{5}{2}
x_S=\frac{x_A+x_B}{2}=\frac{4+1}{2}=\frac{5}{2}=2\frac{1}{2}
y_S=\frac{y_A+y_B}{2}=\frac{1+5}{2}=3
S=(2\frac{1}{2},3)=(a,b)
(x-a)^2+(y-b)^2=r^2 równanie okręgu
(x-2\frac{1}{2})^2+(y-3)^2=(\frac{5}{2})^2
(x-2\frac{1}{2})^2+(y-3)^2=\frac{25}{4}
(x-2\frac{1}{2})^2+(y-3)^2=6\frac{1}{4}
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