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how to find the second point of intersection

how do you find the second point of intersection of a line through a circle given the equation of the circle the line and one set of coordinates? thanks
Reply 1
Original post by madfish
how do you find the second point of intersection of a line through a circle given the equation of the circle the line and one set of coordinates? thanks


simultaneous equations

the line with the curve

you will get a quadratic but you already know one root
Original post by madfish
how do you find the second point of intersection of a line through a circle given the equation of the circle the line and one set of coordinates? thanks


Either solve it simultaniously or know it will be on the opposite side of the center.
Reply 3
Original post by TenOfThem
simultaneous equations

the line with the curve

you will get a quadratic but you already know one root

i get a quadratic with 2 squared terms... y^2 and x^2

how do i solve that?
Reply 4
Original post by madfish
i get a quadratic with 2 squared terms... y^2 and x^2

how do i solve that?


simultaneously

you have another equation that says y=
Reply 5
From the equations of a straight line and a circle, substitute the line into the circle:
Unparseable latex formula:

y = mx + c[br]\\[br](x-a)^2 + (y-b)^2 = r^2[br]\\(x-a)^2 + (mx + c - b)^2 = r^2



Then expand:

[br]x22ax+a2+m2x2+mxcmxb+mxc+c2bcmxbbc+b2=r2[br]x^2 - 2ax + a^2 + m^{2}x^2 + mxc - mxb + mxc + c^2 -bc -mxb -bc + b^2 = r^2

Group like terms, rearrange into the form (A)x2+(B)x+C=0(A)x^2 + (B)x + C = 0 and then substitute into the quadratic formula.

That gives you your two values of x, and y = mx + c lets you find the two corresponding values of y.
(edited 11 years ago)
Reply 6
Original post by TenOfThem
simultaneously

you have another equation that says y=

so I solve by substitution then? I was setting both to zero and equating
Reply 7
Original post by madfish
so I solve by substitution then? I was setting both to zero and equating


yes, substitution

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