# How do you write an equation for a circle given center (-8,-7) and tangent to the y-axis?

##### 1 Answer

Oct 9, 2016

#### Explanation:

The standard form of the equation of a circle is.

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

where (a ,b) are the coordinates of the centre and r, the radius.here centre = (-8 ,-7)

#rArra=-8" and " b=-7# Since the y-axis is a tangent then the radius will be the horizontal distance from (-8 ,-7) to the y-axis ( x = 0). That is radius = 8.

substitute values into the standard equation.

#(x-(-8))^2+(y-(-7))^2=8^2#

#rArr(x+8)^2+(y+7)^2=64" is the equation of the circle"#

graph{(x+8)^2+(y+7)^2=64 [-31.6, 31.6, -15.8, 15.8]}