Posted by geometry on Monday, January 24, 2011 at 2:18am.
what are the equation of a line through (8,-3) and passing distance square root of 10 from (3,2)
gggg - Reiny, Monday, January 24, 2011 at 8:45am
To be a "distance of √10 units away from (3,2) means it has to be tangent to the circle
(x-3)^2 + (y-2)^2 = 10
x^2 + y^2 -6x - 4y = -3
let the point of contact be (a,b)
a^2 + b^2 - 6a - 4b = -3 (#1)
slope of radius to (a,b) = (b-2)/(a-3)
slope from (a,b) to (8,-3) = (b+3)/(a-8)
but these two lines are perpendicular, so ...
(b+3)/(a-8) = - (a-3)/(b-2)
which simplifies to
a^2 + b^2 - 11a + b = -18 ,(#2)
subtract #1 - #2
5a - 5b = 15
a - b = 3
a = b+3 (#3)
sub #3 into #2 to get it simplified to
b^2 - 2b - 3 = 0
(b-3)(b+1) = 0
b = 3 or b = -1
a= 6 or a = 2
so (a,b) is either (6,3) or (2,-1)
Now it is easy to find the equation of the two tangents.
Let me know what you got.
gggg - richard lauro, Thursday, December 3, 2015 at 9:45am
3x+y-21=0 and x+3y+1
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