Common Errors in the Exams

[/0]

One I did today:

You can't use Pr(X > a) = Pr(X < -a) unless the normal distribution has mean 0.

[dcc]

- Not inserting || (absolute signs) in a log after an antidiff or diff.

is that part of methods?

Yes, it was in MAV 2007 exam 1, finding definite integral of logs from [-3 to -1] couldnt've been possible without doing ln|x| instead of ln(x). 

To avoid the negative logarithms, just use symmetry and integrate from the other side of the asymptote (accounting for sign changes, etc).

[nerd]

One I did today:

You can't use Pr(X > a) = Pr(X < -a) unless the normal distribution has mean 0.

I made that exact same mistake...probably the same practice exam!

[ReVeL]

Easily...

#1 - not considering the domain of a function when solving/sketching etc.

Shits me up the wall because I keep doing it haha.

[Collin Li]

One I did today:

You can't use Pr(X > a) = Pr(X < -a) unless the normal distribution has mean 0.

I made that exact same mistake...probably the same practice exam!

The general rule is:

[polky]

* When squaring both sides, not checking your solutions to see if they fit into the appropriate domain.

Gah I made that mistake today!

I think it mostly boils down to (as Mao has said) arithmetic errors.

[ed_saifa]

misreading numbers

[Pandemonium]

well my greatest mistake was dying in the exam.
i promise i'll never do that ever again.
everyone had to watch as i writhed in agony on the floor.
shit was SO cash.













other than that, arithmetical errors.

[nerd]

- Not remembering , is always always positive.

I don't get this one...clearly this is one of the mistakes I will be making!

[Collin Li]

- Not remembering , is always always positive.

I don't get this one...clearly this is one of the mistakes I will be making!

You know how is always positive? It's true for any positive number in place of , i.e: , for all real numbers of

[shinny]

I don't think that's what /0 meant though, he didn't mean the range was always greater than zero, but that the base has to be, since otherwise, you end up with a pretty whack graph which doesn't even qualify as a function I think (I'm struggling to visualise it atm; all I see is alternating values from x=1 to x=2 etc, not too sure what happens in between - graphics calcs can't graph it =\).

[bucket]

- Not remembering , is always always positive.

I don't get this one...clearly this is one of the mistakes I will be making!

You know how is always positive? It's true for any positive number in place of , i.e: , for all real numbers of

i still dont get it!

[phagist_]

Well is just a number.. you can replace it with any positive real number and it will not affect the basic shape of the graph.

Try writing out a table of values.. say for at x=1, x=2, x=3, etc... and you will see it keeps increasing toward infinity.

Similarly for x=-1, x=-2, it decreases and approaches zero.

Hence the function of is always greater than zero.

[nerd]

but thats not what /0 meant. He said that for , is always always positive. Not that ...

[Collin Li]

Nah, is the condition. Why would he say " is positive" (tautological)?

He meant that if , then is always positive (i.e: )