Trig Question (1 Viewer)

[bujolover]

I know this seems like a relatively simple enough question, but I cannot get the "right" answer, so please provide the answer, and don't just half-complete the question. I just want to know the answer so that I can confirm whether or not the answer the answer key gives is wrong.

Thanks in advance!

P.S. I actually have another trig question that I can't get an answer for (so the title should actually now be trig questions ), and I thought I might as well post it with this question. Please provide an answer when posting, as well as full working out.

A building stands on level ground. From two points on opposite sides of the building, X and Y, the angles of elevation to the building are 53 degrees and 46 degrees respectively. If the distance between X and Y is 62m, find the height of the building.

 

[dan964]

Skeleton for the first one, I won't do it for you

1. Use the cosine rule to find one the angles (there is a particular one you will need, won't tell you which one)
2. Draw a parallel line through C and call north there M.
3. Let us give the SOUTH direction at the point A; S. (That is N, A, S are all on the same line)
4. Observe that . Find and go from there
(hint use parallel lines)
5. Make sure to get the correct angle in the end

Don't have a calculator on me to do the calculation. But if it is bigger than 65, then it is wrong.

 

[bujolover]

Skeleton for the first one, I won't do it for you

1. Use the cosine rule to find one the angles (there is a particular one you will need, won't tell you which one)
2. Draw a parallel line through C and call north there M.
3. Let us give the SOUTH direction at the point A; S. (That is N, A, S are all on the same line)
4. Observe that . Find and go from there
(hint use parallel lines)
5. Make sure to get the correct angle in the end

Don't have a calculator on me to do the calculation. But if it is bigger than 65, then it is wrong.

I had used the cosine rule to find angle BCA, and I got 49 deg. 46' (nearest min.).
I didn't use MAC (I couldn't understand how it helps answer the question); I used angle MCA, for which I got 65 deg. (using alternate angles with angle SAC as you mentioned)
Then I said that as angle MCA = angle MCB + angle BCA, and angle BCA = 49 deg. 46',
angle MCB + 49 deg. 46' 9.59" (I used the entire value that the calculator displayed) = 65 deg.
Therefore, Bearing = angle MCB = 15 deg. 13' 50.41" (15 deg. to nearest deg.)

But the answer says 035 degrees, and I'm not sure if that's right or not. The working given is:
alpha + 30 deg. + 25 deg. = 90 deg.
alpha = 35 deg.
Therefore, bearing is 035 degrees.

But I don't think 30 is supposed to be in the picture. That's why I just want to confirm what the answer is to know that the answer given in the answers is wrong.

BTW, the given answer to the second question doesn't include working, so I can't even guess where the answer comes from. Plus, the answer I got is not really close to the given one.

 

[He-Mann]

The answer for the first question is wrong.

Their angle BCA is 30 deg. which is wrong and should be ~50 deg. as you computed correctly. It couldn't have been a calculation error on their part as each angle is approximately 50, 60, and 70 deg. which is singificantly above 30 deg. The answer wasn't typed right? Because the number 5 does not lie close to 3 for a typo to occur (assuming regular num-pad).

 

[He-Mann]

For the second question, at least provide your working out or diagram.

Is the answer ~36m?

 

[bujolover]

The answer for the first question is wrong.

Their angle BCA is 30 deg. which is wrong and should be ~50 deg. as you computed correctly. It couldn't have been a calculation error on their part as each angle is approximately 50, 60, and 70 deg. which is singificantly above 30 deg. The answer wasn't typed right? Because the number 5 does not lie close to 3 for a typo to occur (assuming regular num-pad).

No, it was handwritten, so there were definitely no typos going on. I think they misread the diagram they had drawn and thought the 30 n.m. for BA was the angle (30 degrees) they needed.
Thank you for confirming this for me.

 

[bujolover]

For the second question, at least provide your working out or diagram.

Is the answer ~36m?

I got 36.06m (2 dec. pl.), which is basically what you got too, so I can confirm that the answer given (43.3m) is wrong.

This is my diagram anyway, since you asked for it:



Thanks for your help again.

 

[dan964]

I had used the cosine rule to find angle BCA, and I got 49 deg. 46' (nearest min.).
Then I said that as angle MCA = angle MCB + angle BCA, and angle BCA = 49 deg. 46',

Typo on my part.