I know...

[ronnie]

Ok, last time I promise. I have two problems(both deal w/graphs).

#1: How do you find the equation of a line when all they do is provide a graph with the line on it? The line does form a right triangle with the x and y axis.

#2: Find the point(s) of intersection: x^2 + y^2=25, 2x-y=5

I know the x and y squared means its a circle, right? For any of you that wonder, all these questions are from an algebra assessment(which as you can guess, I need to review, lol)

Thanks for all the help!!!!!

 

[tkhunny]

#1: How do you find the equation of a line when all they do is provide a graph with the line on it? The line does form a right triangle with the x and y axis.

The right triangle is a good hint about the SLOPE of the line. If you can also identify one point (maybe the y-intercept), you should be able to find the equation.

#2: Find the point(s) of intersection: x^2 + y^2=25, 2x-y=5

Substitute?
x^2 + y^2=25
2x-y=5 ==> y = 2x - 5
x^2 + (2x-5)^2=25

Solve that for 'x' if possible.

 

[Gene]

Just pick any two points (0,y) and (x,0) are usually easy. The slope is (y₁-y₂)/(x₁-x₂)

Just solve the two equations.
Get y=2x-5 from the second and substitute that for y in the first. Solve for x. Then use that to solve for y. You should get two points where the line goes thru the circle.

PS. Gotta learn to type faster :twisted:

 

[ronnie]

Y'all are the bestest!!!! One question though...on the first problem, how do I accurately pick those two points? Like, I'm looking at the graph right now, and there is no easy points, like say (0,2). The only type I see is like (3,.8).

Thanks Again!!!!

 

[Gene]

In that case pick them as far apart as possible, to minimize the effect of error. Just use your best guess. If the graph has unit squares you should be within <u>+</u>.2 at the worst, probably within <u>+</u>.1 If you take it where it crosses a line you get one of them exact.