How do you write an equation for for circle given that the endpoints of the diameter are (-2,7) and (4,-8)?

2 Answers
Jan 9, 2018

(x-1)^2+(y+1/2)^2=261/4(x1)2+(y+12)2=2614

Explanation:

"given the endpoints of the diameter then the centre is at"given the endpoints of the diameter then the centre is at
"the midpoint and the radius is the distance from the "the midpoint and the radius is the distance from the
"centre to either of the 2 endpoints"centre to either of the 2 endpoints

"the equation of a circle in standard form is"the equation of a circle in standard form is

color(red)(bar(ul(|color(white)(2/2)color(black)((x-a)^2+(y-b)^2=r^2)color(white)(2/2)|)))

"where "(a,b)" are the coordinates of the centre and r "
"is the radius"

"midpoint "=[1/2(-2+4),1/2(7-8)]=(1,-1/2)

"to calculate the radius use the "color(blue)"distance formula"

•color(white)(x)d=sqrt((x_2-x_1)^2+(y_2-y_1)^2)

"let "(x_1,y-1)=(4,-8)" and "(x_2,y_2)=(1,-1/2)

d=sqrt((1-4)^2+(-1/2+8)^2)

color(white)(d)=sqrt(9+225/4)=sqrt261/2

(x-1)^2+(y+1/2)^2=(sqrt261/2)^2

rArr(x-1)^2+(y+1/2)^2=261/4larrcolor(blue)"equation of circle"

Jan 19, 2018

Therefore, equation of the given circle is

color(red)((x - 1)^2 + (y + (1/2))^2 = (8.0777)^2)

Explanation:

enter image source here

Center coordinates O ((4-2)/2, (-7+8)/2) = O(1, -(1/2)

diameter /2 = radius = r = sqrt((4+2)^2 + (-8-7)^2) /2 = color(blue)(8.0777)

Standard equation of a circle is

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

Therefore, equation of the given circle is

color(red)((x - 1)^2 + (y + (1/2))^2 = (8.0777)^2)