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# C1 watch

1. Hiya, I need help pleeease on question no. 12 part ii (on the pdf attached)

I just don't understand it and would appreciate help (like i dont know what numbers to put into the A=1/2 bh formulae)

Thankyou

(the answers are there if you scrolll down but i still dont understand it)
Attached Images
2. jan 07.pdf (576.1 KB, 87 views)
3. The base length is the part between the y-intercepts.
The height is from the y axis to the intersection of the two lines
4. (Original post by Potassium^2)
The base length is the part between the y-intercepts.
The height is from the y axis to the intersection of the two lines
Yes but what numbers would i use? :P

could you also tell me how you get them numbers (for the a=1/2bh formulae) plz?. thanks very much
5. Have you worked out the Point M?
For the y-intercept values set x=0 in each of the equations
6. (Original post by TheWonderKid)
Yes but what numbers would i use? :P

could you also tell me how you get them numbers (for the a=1/2bh formulae) plz?. thanks very much
If you can't visualise it, one way of doing this is to split the triangle up into two.

You can clearly see two triangles, which you can find the area of separately and then add together.

You can see that you would need to find where the lines cross the y axis in order to find the height (you get the value of the "base" from the first part of the question).

Hopefully you'll know how to find the equation of a straight line in the form y=mx+c. You'll have to find the equations of both lines, AB and the other one, before working out the y intercepts.

When the line crosses the y axis, x=0 (all x values are 0 if you look along the y axis).

So when you have both equations, let x=0 and find the y value to find the separate heights. Then you can find 1/2bh for each triangle and add them together.

--------------

If you don't know how to find the equation of a straight line given a point, here is one example:

Points A (1, 5) and B (5, 3) are two points on a straight line. Find the equation of the line in the form y=mx+c

First find the gradient, m, which is basically change in y divided by change in x.
For this example, that would be

Plop this into y=mx+c to give you y=-0.5x+c
Now we need to find c. Pick any point they give you - i'm gonna pick A (1, 5) - and substitute the values in:

5=-0.5(1)+c
5=-0.5+c
c=5.5

So plop this into y=-0.5x+c and you'll get y=-0.5x+5.5 as the equation of the line.

Find where AB crosses the y axis

y=-0.5x+5.5

Let x=0
y=-0.5(0)+5.5
y=5.5

AB crosses the y axis at (0, 5.5)
7. (Original post by Potassium^2)
Have you worked out the Point M?
For the y-intercept values set x=0 in each of the equations
yeah, point m is (3,6)

And the height would be 7.5 because

y= 12-2x and y=1/2x + 4.5 are the two lines

At y-intcpt, x=0 so it would be 12-4.5 which is 7.5 (this is the base length?)

And how do i find the other length? sorry
8. (Original post by Chelle-belle)
If you can't visualise it, one way of doing this is to split the triangle up into two.

You can clearly see two triangles, which you can find the area of separately and then add together.

You can see that you would need to find where the lines cross the y axis in order to find the height (you get the value of the "base" from the first part of the question).

Hopefully you'll know how to find the equation of a straight line in the form y=mx+c. You'll have to find the equations of both lines, AB and the other one, before working out the y intercepts.

When the line crosses the y axis, x=0 (all x values are 0 if you look along the y axis).

So when you have both equations, let x=0 and find the y value to find the separate heights. Then you can find 1/2bh for each triangle and add them together.

--------------

If you don't know how to find the equation of a straight line given a point, here is one example:

Points A (1, 5) and B (5, 3) are two points on a straight line. Find the equation of the line in the form y=mx+c

First find the gradient, m, which is basically change in y divided by change in x.
For this example, that would be

Plop this into y=mx+c to give you y=-0.5x+c
Now we need to find c. Pick any point they give you - i'm gonna pick A (1, 5) - and substitute the values in:

5=-0.5(1)+c
5=-0.5+c
c=5.5

So plop this into y=-0.5x+c and you'll get y=-0.5x+5.5 as the equation of the line.

Find where AB crosses the y axis

y=-0.5x+5.5

Let x=0
y=-0.5(0)+5.5
y=5.5

AB crosses the y axis at (0, 5.5)
Oh yes that's a good idea, so would the area of the first triangle be 9? (1/2 * 6 * 3) thanks for your help ppl
9. (Original post by TheWonderKid)
Oh yes that's a good idea, so would the area of the first triangle be 9? (1/2 * 6 * 3) thanks for your help ppl
Yep
10. (Original post by Chelle-belle)
Yep
Hey, if the area of the top triangle is 9, then am i making a mistake on the second
triangle because:

• The length of the triangle going up the y-axis is 2 right?
• But what about the length of the line from A to M? (i thought this was

I got for the top triangle---> 6* 3 * 0.5 = 9
And for the second triangle i got 2 * 3 * 0.5 =3

However, when i add them together i get 12. Shouldn't the answer (according to the MS) be 11.25 or 45/4?

Thankyou sooooo much for your help. I'll rep both of you (if i know how to, that is lol)
11. (Original post by TheWonderKid)
Hey, if the area of the top triangle is 9, then am i making a mistake on the second
triangle because:

• The length of the triangle going up the y-axis is 2 right?
• But what about the length of the line from A to M? (i thought this was

I got for the top triangle---> 6* 3 * 0.5 = 9
And for the second triangle i got 2 * 3 * 0.5 =3

However, when i add them together i get 12. Shouldn't the answer (according to the MS) be 11.25 or 45/4?

Thankyou sooooo much for your help. I'll rep both of you (if i know how to, that is lol)
A is not the point of intersection - it is the end of the line AB
12. (Original post by Chelle-belle)
A is not the point of intersection - it is the end of the line AB
Ahh i've got it finally!

1/2 * 6 * 3= 9

and 1/2 * 1.5 * 3 (6-4.5 the sum used) This gives you 2.25

9 + 2.25 = 11.25

Again thanks very much!

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