Trig question

S

Sabi

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Oct 12, 2020
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Hey guys,

So I've been working through a math exercise book and this is one of the questions.

I've just been told my answers are incorrect...

The funny thing is though I came up with the exact same answers that are in the solution page of the book so I'm obviously quite confused.

Can the book be wrong? seems like an amazing coincidence that I'd come out with identical answers to the book.

Can anyone see clear errors in my work? The questions are to find the angle theta and the dimension A.

I have to say though. Logically thinking these answers do seem unlikely from a scale point of view.

20201116_182749.jpg
 
You say, "I came up with the exact same answers that are in the solution page of the book", but don't tell us what they are; you say, "I've just been told my answers are incorrect", but don't say who said that or what they said. (As has been pointed out, you also didn't show the problem, so we can't be sure which of the numbers in your work you should have reported.) So I can't say whether the answers you gave are the right answers to the questions you were to answer.

I'm guessing that you just entered numbers into a computer and were told that at least one number was wrong, but not which; but problems on a computer usually aren't identical to one in a book, so I'm unsure of the context here.

Looking at your work:

Just above "8B", you claim to be finding theta, and then say you found "dovetail angle", whatever that means. It is not theta, which is actually its complement, 24.22.

Under 8B, you find 24.22 but then show 22.228 on the next line; I think you (correctly) used the 24.22. But that isn't the angle theta shown on the picture. Your 12.114 is correct, but you then change it to 12.115 (it is really 12.11387).

Several times you used sines where I would use a tangent more efficiently, but that isn't an error.

On the whole, I'd say your work is correct, but there's a good chance you reported the wrong numbers. When you show the problem exactly as given to you, and the answers given in the book, and what answers you reported, we may be able to resolve the mystery.

EDIT after seeing book's answers: I wonder if both you and the book made the same simple mistake, reporting the complement of theta.

Or, I may have made a mistake somewhere, as things don't quite seem consistent, and I did too much in my head.
 
Last edited:
Dr.Peterson said:
You say, "I came up with the exact same answers that are in the solution page of the book", but don't tell us what they are; you say, "I've just been told my answers are incorrect", but don't say who said that or what they said. (As has been pointed out, you also didn't show the problem, so we can't be sure which of the numbers in your work you should have reported.) So I can't say whether the answers you gave are the right answers to the questions you were to answer.

I'm guessing that you just entered numbers into a computer and were told that at least one number was wrong, but not which; but problems on a computer usually aren't identical to one in a book, so I'm unsure of the context here.

Looking at your work:

Just above "8B", you claim to be finding theta, and then say you found "dovetail angle", whatever that means. It is not theta, which is actually its complement, 24.22.

Under 8B, you find 24.22 but then show 22.228 on the next line; I think you (correctly) used the 24.22. But that isn't the angle theta shown on the picture. Your 12.114 is correct, but you then change it to 12.115 (it is really 12.11387).

Several times you used sines where I would use a tangent more efficiently, but that isn't an error.

On the whole, I'd say your work is correct, but there's a good chance you reported the wrong numbers. When you show the problem exactly as given to you, and the answers given in the book, and what answers you reported, we may be able to resolve the mystery.

EDIT after seeing book's answers: I wonder if both you and the book made the same simple mistake, reporting the complement of theta.
Click to expand...

I have now posted both the question and answers straight from the book.

My tutor told me it was incorrect. Pretty difficult to get decent feedback currently as everything is remote.

Thanks for your reply.
 
Dr.Peterson said:
EDIT after seeing book's answers: I wonder if both you and the book made the same simple mistake, reporting the complement of theta.

Or, I may have made a mistake somewhere, as things don't quite seem consistent, and I did too much in my head.
Click to expand...

Time to have another go then!
 
Both of the book's answers are wrong. As I said, their theta is the complement of theta; but using the correct theta, I get a very different number for A.

I would guess that they just made the same easy mistake as you, using the wrong theta and therefore getting the wrong A. But your ideas are all correct. Just apply them to the right number!
 
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