# maths-urgently needed

posted by .

find the equation of circle
if the line 2x - y +1 = 0 touches the circle at the point (2,5) and the center of the circle lies on the line x+y -9 =0

• maths-urgently needed -

If the line touches the circle, then the line from (2,5) to the center is perpendicular to the line y=2x+1, so it has slope -1/2.

So, the line through (2,5) with slope -1/2 is

y-5 = -1/2 (x-2)
y = -1/2 x + 6

This line passes through the center of the circle, so

-1/2 x + 6 = 9-x
x=6

(6,3) is the center of the circle.
The radius is the distance from (6,3) to (2,5) = √20

The circle is thus

(x-6)^2 + (y-3)^2 = 20

Just as a final check:
The distance from (6,3) to the line 2x-y+1 = 0 is |2*6 - 3 + 1|/√5 = 10/√5 = 2√5 = √20

## Similar Questions

1. ### calc

standard equation of circle concentric with X^2+Y^2-2X-8Y+1=0 and tangent to line 2X-Y=3 Complete the squares to find the center of the circle. X^2+Y^2-2X-8Y+1=0 (x-1)^2+(y-4)^2 - 16 =0 The center is (1,4) and the radius for the given …
2. ### steev

can u help this the qustion is : A circle passes through the points (1,4)&(5,0) and its centre lies on the line x+y-3=0.Find (i) the equation of the circle and it parametric equations . (ii) the centre,diameter and area of the circle …
3. ### math

can u help this the qustion is : A circle passes through the points (1,4)&(5,0) and its centre lies on the line x+y-3=0.Find (i) the equation of the circle and it parametric equations . (ii) the centre,diameter and area of the circle …
4. ### GEOMETRY INSCRIBED ANGLES MULTIPLE CHOICE QUESTION

segment BC is tangent to circle A at B and to circle D at C. (Not drawn to scale) AB=10 BC=25 and DC=3. Find AD to the nearest tenth. Hint: Draw an auxiliary line from D to segment BA. {There are two circles, the larger one has point …
5. ### mathematics

The circle x2-2x+y2-4y-4=0 lies on the cartesian plane,question 2.1.1 equation of new circle which is the rotation of original circle through 180 degree around the origin...2.1.2 find equation of another circle which is the translation …
6. ### mathematics

The circle x2-2x+y2-4y-4=0 lies on the cartesian plane,question 2.1.1 equation of new circle which is the rotation of original circle through 180 degree around the origin...2.1.2 find equation of another circle which is the translation …
7. ### Math

find the equation of the circle whose centre lies on the line 5x-2y=9 and the circle touches both the positive axes
8. ### Math

The point P = (4, 3) lies on the circle x2 + y2 = 25. Find an equation for the line that is tangent to the circle at P. This line meets the x-axis at a point Q. Find an equation for the other line through Q that is tangent to the circle, …
9. ### Math

The point P = (4, 3) lies on the circle x2 + y2 = 25. Find an equation for the line that is tangent to the circle at P. This line meets the x-axis at a point Q. Find an equation for the other line through Q that is tangent to the circle, …
10. ### sir steve reiny damon bob maths help steve!!!

Point P(2,1) and Q(4,-5) lie on a circle. If line 2x-y-13=0 is a tangent to the circle at Q, what is (*) Coordinates of the center of the circle; (*) Equation of the circle. (*) Sketch out your circle. Step

More Similar Questions