Mega A Level Maths Thread MK II

Oh, Okay thanks

Sorry to be a pain but I can't do probability!!!!!!

For question 6c, why don't you include the outside of the Venn Diagram when finding the probability of A and not B? Surely the outside counts as the not B bit?

Thanks you're all amazing, bye.

Hmm, stuck on a log question:

Solve for x:

$5^{x} = 3^{x-1}$

So far, I have:

$xlog5 = xlog3 - log3$

but I have no idea where to go from there . Help?

Rearrange then factor out the x

How could I have not spotted that?! Thanks!

Can anyone help me with this question please...

Show that cotx - sin2x = cotxcos2x for 0<x<180 (3 marks)


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Is this a show that or a solve for x?

First off rewrite cot(x) in terms of sin and cos, then write the LHS as one fraction

First part is show that, second part asks to solve... Do I need to change sin2x into 2sinxcosx?


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Yep:
So you've got:
$\frac{\cos(x)}{\sin(x)} - 2\sin(x)\cos(x)$
What now?

Today has gone pretty well - S in STEP III mock, as well as 75/75 in C4 mock.

I'm so confused :/ I've got up to that bit


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Rewrite as:
$\dfrac{\cos(x)- 2\sin^2(x)\cos(x)}{\sin(x)}$
Can you see what I did here, and what the next step is?

Yeah that makes sense, still don't know what to do next though D: change 2sin^2x into 2(1-cos^2x) ? I really don't know..
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Consider a double angle expression for cos(2x) . . .

There's only a cos2x on the RHS though isn't there?


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$\cos(2x)= \cos^2(x) - \sin^2(x) = (1 -\sin^2(x)) - sin^2(x)$
You can finish up

1 - 2sin^2x but I don't understand where that fits in?


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