Thread: Find the coordinates...

Find the coordinates of the point(s) of intersection of the line y = 2x + 5 with the circle (x - 3)^2 + (y + 4)^2 = 50.

Where are you stuck ?

Originally Posted by flyingsquirrel

Where are you stuck ?

From the beginning. I don't know what to do.

Do you think you can provide me a complete worked out solution to this?

Well you have two equations and two unknowns. Start by plugging in y = 2x + 5 into the other equation, like this:
.

Solve for x, and when you're done, plug that back into y = 2x + 5 to solve for y. (You may get two answers for x, so plug each answer in to get a different y.)


01

(x - 3)^2 + (2x + 5 + 4)^2 = 50
(x - 3)^2 + (2x + 9)^2 = 50
x^2 - 6x + 9 + 4x^2 + 36x + 81 = 50
5x^2 + 30x + 90 = 50
5x^2 + 30x + 40 = 0

Using the quadratic formula:

x = -2 or x = -4

y = 2 (-2) + 5
= 1

or

y = 2(-4) + 5
= -3

Am I right so far? If so, what do I do next?

Originally Posted by Mr Rayon

x = -2 or x = -4

y = 2 (-2) + 5
= 1

or

y = 2(-4) + 5
= -3

Am I right so far? If so, what do I do next?

That's it. You have the points: (-2, 1) and (-4, -3).

BTW, you didn't have to use the quadratic formula -- the quadratic was factorable.




01