# Thread: 3U Homework - Help!

1. ## 3U Homework - Help!

Hey guys, I need help with some Exam Revision - its really confusing...

a) The point M(-3,8) divides the interval joining A(-4,-9) and B(5,9) externally in the ratio k:1. Find the value of k.

b) Sydney Tower stands on a level ground, Three observers P,Q and R are observing Sydney tower from the ground. P is due north of Sydney Tower, R is due east of Uluru, and Q is on the line of sight from P to R and between them. The angles of elevation to the top of Sydney Tower from P, Q and R are 26 degrees, 28 degrees and 30 degrees, respectively. Find the bearing of Q from Sydney Tower. c) The angle between the lines y = mx and y = 1/2 x is 45 degrees. Find the exact value of m.

I've tried, but nothing is working - If anyone could assist me in understanding these that would be terrific. Thank you for your time.  Reply With Quote

2. ## Re: 3U Homework - Help!

a) Use the formula

Calculate the point using your ratio and your two points (be careful, order matters).

Then compare your point to the one given and you should be able to find .

c) Using the formula

We get:

From here you can take cases, or you can use the definition and square both sides to solve for . Originally Posted by Heresy Q is on the line of sight from P to R and between them.
Should that be read as "Q in the middle of P and R"? Or is it just saying the same thing twice?  Reply With Quote

3. ## Re: 3U Homework - Help! Originally Posted by fan96 a) Use the formula

Calculate the point using your ratio and your two points (be careful, order matters).

Then compare your point to the one given and you should be able to find .

c) Using the formula

We get:

From here you can take cases, or you can use the definition and square both sides to solve for .

Should that be read as "Q in the middle of P and R"? Or is it just saying the same thing twice?
My interpretation is that it is saying in the middle  Reply With Quote

4. ## Re: 3U Homework - Help! Originally Posted by Heresy My interpretation is that it is saying in the middle Given that ...

Let the height of Sydney Tower be .

(since the height of a tower won't change its bearing, we can use in our calculations but it will not appear in the final answer)

1. Find in terms of .

2. Noting that is a right-angled, find and hence .

3. Then use the cosine rule to find .  Reply With Quote

5. ## Re: 3U Homework - Help! Originally Posted by fan96  Given that ...

Let the height of Sydney Tower be .

(since the height of a tower won't change its bearing, we can use in our calculations but it will not appear in the final answer)

1. Find in terms of .

2. Noting that is a right-angled, find and hence .

3. Then use the cosine rule to find .
Mate you're a legend thank you so much, I really appreciate it!!  Reply With Quote

6. ## Re: 3U Homework - Help! Originally Posted by fan96  Given that ...

Let the height of Sydney Tower be .

(since the height of a tower won't change its bearing, we can use in our calculations but it will not appear in the final answer)

1. Find in terms of .

2. Noting that is a right-angled, find and hence .

3. Then use the cosine rule to find .
I'm sorry to ask but can you help me with Part 2 of that solution process please? I'm utterly useless...  Reply With Quote

7. ## Re: 3U Homework - Help! Originally Posted by Heresy I'm sorry to ask but can you help me with Part 2 of that solution process please? I'm utterly useless...
Don't think negatively like that. Just keep practicing and you'll improve.

If you found then use Pythagoras' theorem:

and of course, .  Reply With Quote