# Thread: gradients and y-intecept

1. ## gradients and y-intecept

This question may be a bit vague but considering i cant draw the graph i hope someone can still help

I need to find the gradient and y-intercept of a line given, than i need to write the equation of the line.

Now am i correct in saying the y-intercept is where the line crosses on the y point?

If so than it crosses at -1

so how do i than find the gradient if that is all im given?

2. Originally Posted by BsMummy

Now am i correct in saying the y-intercept is where the line crosses on the y point?
Let's call it the y-axis, do you have the point where your line crosses the x-axis?

This can help you find the gradient

3. Originally Posted by BsMummy
This question may be a bit vague but considering i cant draw the graph i hope someone can still help

I need to find the gradient and y-intercept of a line given, than i need to write the equation of the line.

Now am i correct in saying the y-intercept is where the line crosses on the y point?

If so than it crosses at -1

so how do i than find the gradient if that is all im given?
Yes, you are correct about the y-intercept. In order to find the gradient of a line you need two points. If you know the y-intercept, then you have the point (0,-1). But you have to have another point to find the gradient. What other information are you given? There must be more. Are you given a graph of the line?

4. Originally Posted by pickslides
Let's call it the y-axis, do you have the point where your line crosses the x-axis?

This can help you find the gradient

The line crosses the x-axis at 4

5. Originally Posted by adkinsjr
Yes, you are correct about the y-intercept. In order to find the gradient of a line you need two points. If you know the y-intercept, then you have the point (0,-1). But you have to have another point to find the gradient. What other information are you given? There must be more. Are you given a graph of the line?

would finding the x-axis help? if so that would be 4

so now i have (0,-1) and (0,4)

is that all i will need to find the gradient?

yes i am given a graph of the line but i dont know how to but that graph up on here!

6. Originally Posted by BsMummy

so now i have (0,-1) and (0,4)
No, you really have (0,-1) and (4,0)

the gradient $\displaystyle m = \frac{y_2-y_1}{x_2-x_1}$

where $\displaystyle (0,-1) = (x_1,y_1)$ and $\displaystyle (4,0) = (x_2,y_2)$

7. okay so i have worked out that the gradient is .5 or 1/2 - but i worked that out by looking at the graph and counting how many sqaures i went up from the y intercept to the x intercept

so now that i have the gradient at .5 or 1/2 how do i write the equation of the line?

8. Originally Posted by BsMummy
okay so i have worked out that the gradient is .5 or 1/2 - but i worked that out by looking at the graph and counting how many sqaures i went up from the y intercept to the x intercept

so now that i have the gradient at .5 or 1/2 how do i write the equation of the line?
The general form is $\displaystyle y=mx+b$. So the line will have the equation $\displaystyle y=\frac{1}{2}x+b$ where b is the y-intercept. Since b=-1, the line is $\displaystyle y=\frac{1}{2}x-1$

9. okay i used the way to find the gradient that pickslides gave and now im getting 1/4 - which im thinking would be the right answer since im no maths genious!

10. Originally Posted by adkinsjr
The general form is $\displaystyle y=mx+b$. So the line will have the equation $\displaystyle y=\frac{1}{2}x+b$ where b is the y-intercept. Since b=-1, the line is $\displaystyle y=\frac{1}{2}x-1$

thankyou - i will just change the 1/2 to a 1/4 since i think that is the gradient - thanks Heaps to you and Pickslides

11. Originally Posted by BsMummy
thankyou - i will just change the 1/2 to a 1/4 since i think that is the gradient - thanks Heaps to you and Pickslides
Yep.