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write the equation of the line tangent to the circle x^2 +y^2=169 at the point (-5,12)

 Jul 19, 2016

Best Answer 

 #2
avatar+129840 
+5

write the equation of the line tangent to the circle x^2 +y^2=169 at the point (-5,12)

 

This is a circle of radius 13 that is centered at the origin

 

The slope of the line segment drawn from the circle's center to the point (-5/12) = the radius   = -12/5

 

And since a tangent line to a circle at a given point is always perpendicular to the radius at that point, the slope of the tangent line =    5/12

 

And the equation of the tangent line is as follows:

 

y - 12= (5/12)(x -  -5)    simplify

 

y - 12   = (5/12)x + 25/12

 

y = (5/12)x + 169/12

 

Here's a graph :  https://www.desmos.com/calculator/xefjptaopf

 

 

cool cool cool

 Jul 20, 2016
 #1
avatar+118659 
+5

Find the gradient of the radius that touches the tangent.

The gradient of the tangent is the negative reciprocal.

Use the point and the gradient to determine the equation.

 Jul 19, 2016
 #2
avatar+129840 
+5
Best Answer

write the equation of the line tangent to the circle x^2 +y^2=169 at the point (-5,12)

 

This is a circle of radius 13 that is centered at the origin

 

The slope of the line segment drawn from the circle's center to the point (-5/12) = the radius   = -12/5

 

And since a tangent line to a circle at a given point is always perpendicular to the radius at that point, the slope of the tangent line =    5/12

 

And the equation of the tangent line is as follows:

 

y - 12= (5/12)(x -  -5)    simplify

 

y - 12   = (5/12)x + 25/12

 

y = (5/12)x + 169/12

 

Here's a graph :  https://www.desmos.com/calculator/xefjptaopf

 

 

cool cool cool

CPhill Jul 20, 2016
 #3
avatar+118659 
+5

max.Dave

What was wrong with my answer Max ?

Do you need to be spoon fed the answer?  Is this so you can just copy it as your own work?

 

I gave you a good outline.  If you needed the dots joined for you you could have just asked.

I am always prepared to give a great deal of my time to students who are actually trying to learn!

 

Thanks for the point recognition Michael :)

 Jul 21, 2016

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