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March 29, 2015

March 29, 2015

Posted by **jojo** on Thursday, March 5, 2009 at 8:25pm.

x2+y2=18

x+y=4

- math b -
**Damon**, Thursday, March 5, 2009 at 8:26pmDo you mean the circle

x^2+y^2 = 18 ?

- math b -
**jojo**, Thursday, March 5, 2009 at 8:34pmyes

- math b -
**Damon**, Thursday, March 5, 2009 at 8:36pmMaking that assumption, we are looking for where the straight line:

y = -1x + 4

which has a slope of -1 and goes through (0,4) and (4,0)

hits the circle with center at the origin and radius 3 sqrt 2 which is about 4.24

Sketch a graph so we will get an idea of how the solution should look.

So

substitute y = -x + 4 into the circle

x^2 + (-x+4)^2 = 18

x^2 + x^2 - 8 x + 16 = 18

2 x^2 -8 x -2 = 0

x^2 - 4 x -1 = 0

x = (1/2)[ 4 +/- sqrt (16 +4)]

x = (1/2) [ 4 +/- 2 sqrt 5]

x = 2 +/- sqrt 5

find the y for each of those x values

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