SOLUTION: Find the equations of the circles passing through the points(2,3)and the lines 3x-4y+1=0,4x+3y-7=0 touching

Algebra ->  Circles -> SOLUTION: Find the equations of the circles passing through the points(2,3)and the lines 3x-4y+1=0,4x+3y-7=0 touching       Log On


   



Question 983085: Find the equations of the circles passing through the points(2,3)and the lines
3x-4y+1=0,4x+3y-7=0 touching

Answer by Edwin McCravy(20059) About Me  (Show Source):
You can put this solution on YOUR website!
Find the equations of the circles passing through the points(2,3) tangent
to the lines:
3x-4y+1=0, 4x+3y-7=0



Let the center be (h,k) the the radius is the perpendicular distance from
(h,k) to each line.  So using the formula:

d = abs%28Ax%5B1%5D%2BBy%5B1%5D%2BC%29%2Fsqrt%28A%5E2%2BB%5E2%29

r = %283h-4k%2B1%29%2Fsqrt%283%5E2%2B%28-4%29%5E2%29%22%22=%22%22%284h%2B3k-7%29%2Fsqrt%284%5E2%2B3%5E2%29

r = %283h-4k%2B1%29%2F5%22%22=%22%22%284h%2B3k-7%29%2F5

And since (2,3) is on the circle, the distance from (h,k) to (2,3) also
equals r.  use

d=sqrt%28%28x%5B2%5D-x%5B1%5D%29%5E2%2B%28y%5B2%5D-y%5B1%5D%29%5E2%29

r=sqrt%28%28h-2%29%5E2%2B%28k-3%29%5E2%29

r%5E2=%28h-2%29%5E2%2B%28k-3%29%5E2

Square all three sides of 

r%5E2%22%22=%22%22%283h-4k%2B1%29%2F5%22%22=%22%22%284h%2B3k-7%29%2F5

r%5E2%22%22=%22%22%283h-4k%2B1%29%5E2%2F25%22%22=%22%22%284h%2B3k-7%29%5E2%2F25

So we have the two equations:

%28h-2%29%5E2%2B%28k-3%29%5E2%22%22=%22%22%283h-4k%2B1%29%5E2%2F25

%28h-2%29%5E2%2B%28k-3%29%5E2%22%22=%22%22%284h%2B3k-7%29%5E2%2F25

Its a lot of work but when you solve those for h and k, you get

h=2, k=8, r=5   and    h=6%2F5, k=12%2F5, r=1

So the circles's equations are

%28x-2%29%5E2%2B%28y-8%29%5E2=25 and %28x-6%2F5%29%5E2%2B%28y-12%2F5%29%5E2=1

Edwin