Linear equation

Quote:

Originally Posted by abc

this is the question:

Given that A(0,-3) and B(-10,-28) are two points that lie on a straight line in x and y space, find:
(a) The slope of the line
(b) The intercept
(c) The equation for the straight line
(d) Sketch the line

I uset his formula c = y1 - y2 / x1 - x2 = 25/10

so y = a - 25/10x

the slope of the line is 25/10x

how do i find the intercept( is there a formuala to this), and also the quation for the stright line.

I am assuming the "d" will be answered by doing "c" should that shouldn't be a problem.

I would really appreciate your help.

Im not sure about that form, but i have heard of it, just never learned it. You could use

y = mx + c

Where m is the gradient and c is the y-intercept.

1) Slope of line

This is the gradient, which is verticle change divided by horizontal change, which if you use your A and B co-ordinates comes to 2.5x. This is what you got, which was 25/10x, but just simplified.

2) Intercept and Equation of line

Finding the intercept will basicly find the equation of the line. We know so far that y = 2.5x + c, as the gradient is m, which is 2.5. We then sub in the x and y values for either A or B. If we use A,

-3 = 2.5(0) + c
Therefore c = -3

This means we can sub -3 into c to get the equation of the line.

y = 2.5x -3

4) Scetching the line

This part is quite simple. Just draw a line that goes through points A (0,-3) and B (-10,-28). You can also mark on the line the y intercept, which should be - 3.