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Find the point of intersection, if any , between each circle and line with the equations given?

 

x^2 + y^2 = 25: y = x

 

(x+4)^2 + (y-3)^2 = 25: y = x + 2

 Feb 4, 2016

Best Answer 

 #2
avatar+129850 
+5

(x+4)^2 + (y-3)^2 = 25: y = x + 2        sub the second equation into the first for y

 

(x + 4)^2  + ( x + 2 - 3)^2  = 25

 

(x + 4)^2 + (x - 1)^2  = 25     expand the left side

 

x^2 + 8x + 16 + x^2 - 2x + 1   = 25     simplify

 

2x^2 + 6x + 17 = 25      subtract 25 from both sides

 

2x^2 + 6x - 8  = 0      divide through by 2

 

x^2 + 3x - 4  =  0     factor

 

(x - 1) ( x + 4)  = 0       and setiing each factor to 0, we have that  x  = 1  and x = -4

 

So when x = 1, y= 1 + 2 = 3     and when x = -4,  y= -4 + 2  = -2

 

So....the intersection points are  (1, 3)  and  ( -4, -2)

 

 

cool cool cool       

 Feb 4, 2016
 #1
avatar+129850 
+5

x^2 + y^2 = 25: y = x     

 

Put the second equation into the first for y   and we have

 

x^2 + x^2  = 25

 

2x^2  = 25    divide both sides by 2

 

x^2  = 25/2          take the square root of both sides

 

x^2  = [ +/-] 5/sqrt( 2)

 

And since x = y   the intersection points are :

 

(5/sqrt(2), 5/sqrt(2) )  and   (-5/sqrt(2), -5/sqrt(2) )

 

 

cool cool cool

 Feb 4, 2016
 #2
avatar+129850 
+5
Best Answer

(x+4)^2 + (y-3)^2 = 25: y = x + 2        sub the second equation into the first for y

 

(x + 4)^2  + ( x + 2 - 3)^2  = 25

 

(x + 4)^2 + (x - 1)^2  = 25     expand the left side

 

x^2 + 8x + 16 + x^2 - 2x + 1   = 25     simplify

 

2x^2 + 6x + 17 = 25      subtract 25 from both sides

 

2x^2 + 6x - 8  = 0      divide through by 2

 

x^2 + 3x - 4  =  0     factor

 

(x - 1) ( x + 4)  = 0       and setiing each factor to 0, we have that  x  = 1  and x = -4

 

So when x = 1, y= 1 + 2 = 3     and when x = -4,  y= -4 + 2  = -2

 

So....the intersection points are  (1, 3)  and  ( -4, -2)

 

 

cool cool cool       

CPhill Feb 4, 2016

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