Inexistence wrote:
Hey everyone, I'm having trouble with my math work and the equation of a straight line. Just so you know I'm only a 12 year old so please don't tell me any stuff I won't understand.
My teacher told us stuff and I didn't understand a bit of it and she wouldn't explain it to me again.
I have a horizontal line along these axis, running on x axis from -4 to -2.5 (3 centimeter boxes across) it is at 2 on the y axis. What I don't get is what to figure out. My teacher said something about triangles but I don't understand. Also, we have to use the equation y=mx+b as a basis.
I need help quickly please.
I'll try to explain it as simply as I can:
Have you ever heard of rise over run? The idea is, you build a right triangle out of your line, with the height being perfectly vertical and the base being perfectly horizontal. The actual line segment you use is the hypotenuse. It doesn't matter what segment of the line you use, but it's usually easiest to make it so that all of the numbers are whole. If possible, that is.
The next step is determining the slope from that. You go rise/run, or vertical length over horizontal length. remember, if you have a line that goes downwards, the slope is negative. The slope becomes the
m in y=mx+b. NOTE: A vertical line has undefined slope. A horizontal line has a slope of 0.
If you don't have a line, but instead have two points that the line passes through, use the following formula: (y
2-y
1)/(x
2-x
1). In other words, you take the y value of the second point, subtract the y value of the first point, do the same with x (make sure you keep them in order!), and then divide your new y by x. That will get you your m value.
The second step: determining
b. Take one of the points you used to determine the slope. (If you started with the line, just use any point on the line). Multiply the x value from the point by m, and then subtract it from the y value of the same point. For example: If you know the slope of a line is 3, and it passes through (4,17), you go 4*3=12, then 17-12=5. Your b value would be 4. NOTE: You can get a negative value here too. Be careful.
Third step: determine the equation. Take your y=mx+b, and replace the m with your slope or m value, and the b with your b value from above. Remember, if you get a negative value for either of these, you have to designate that. So, from the problem above, you have a slope of 3, and a b value of 5. Your equation is: y=3x+5.
It may look complicated, but it's easy once you practice it.