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Mega A Level Maths Thread - Mark IV

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Original post by RoyalBlue7

...

I've seen that question asked on here a lot of times. Trust me, Edexcel won't penalise you for using the cross product on a C4 paper. :smile:

:smile:

(edited 9 years ago)

OP

Original post by Khallil

I've seen that question asked on here a lot of times. Trust me, Edexcel won't penalised you for using the cross product on a C4 paper. :smile:

:smile:

Isn't that unfair on candidates who don't have access to these methods?

I say that having integrated on GCSE papers for area under a curve lol

Original post by L'Evil Fish

...

Life's unfair.

OP

Original post by Khallil

Life's unfair.

Lol ok

Original post by L'Evil Fish

...

It's the truth. Why the lol? :colonhash:

:colonhash:

Edit: Do you really have circa 47,800 posts? :gasp:

:gasp:

(edited 9 years ago)

OP

Original post by Khallil

It's the truth. Why the lol? :colonhash:

:colonhash:

Edit: Do you really have circa 47,800 posts? :gasp:

:gasp:

Because it was so blunt, was funny

I guess I do lmao

Does anyone have any tough M3 or FP2 questions? Preferably MEI but it doesn't really matter. :smile:

:smile:

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Original post by Mattp9850

Does anyone have any tough M3 or FP2 questions? Preferably MEI but it doesn't really matter. :smile:

:smile:

Posted from TSR Mobile

The path of an electron is hypothesised to be modeled by the equation

\dfrac{9}{t^2} + \dfrac{36}{s^2} = 1

Find the acceleration of this electron if it traces around the nucleus in an orbit with time, t, and displacement, s.

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Original post by Arieisit

...

I rearranged for

s^2

and successively differentiated w.r.t.

t

to get:

a = \dfrac{\text{d}^2 s}{\text{d}t^2} = \dfrac{162t}{\left( t^2 - 9 \right)^{\frac{5}{2}}}

Is that correct?

Spoiler

(edited 9 years ago)

Guys I know this seems such a simple question but what are the derivatives of sin(^2)x and cos(^2)x and how are they derived?

Original post by ChemBoss

Guys I know this seems such a simple question but what are the derivatives of sin(^2)x and cos(^2)x and how are they derived?

Use the double angle formulae to get sin^2(x) in terms of sin(x).

Original post by Arithmeticae

...

I think ChemBoss meant the squares of sine of cosine!

Original post by ChemBoss

...

If you're referring to the derivatives of

\sin^2 x

and

\cos^2 x

, then you can use the chain rule!

\dfrac{\text{d}y}{\text{d}x} = \dfrac{\text{d}y}{\text{d}u} \cdot \dfrac{\text{d}u}{\text{d}x}

To begin, we can make a simple substitution if we want to find the derivative of

y = \sin^2 x

:

u = \sin x \implies \dfrac{\text{d}u}{\text{d}x} = \cos x

This means that:

y = u^2 \implies \dfrac{\text{d}y}{\text{d}u} = 2u = 2\sin x

Using the chain rule, we get:

\begin{aligned} \dfrac{\text{d}}{\text{d}x} \left( y \right) = \dfrac{\text{d}}{\text{d}x} \left( \sin^2 x \right) & = \dfrac{\text{d}y}{\text{d}x} = \dfrac{\text{d}y}{\text{d}u} \cdot \dfrac{\text{d}u}{\text{d}x} \\ & = 2\sin x \cos x \end{aligned}

(edited 9 years ago)

Original post by Khallil

I rearranged for

s^2

and successively differentiated w.r.t.

t

to get:

a = \dfrac{\text{d}^2 s}{\text{d}t^2} = \dfrac{162t}{\left( t^2 - 9 \right)^{\frac{5}{2}}}

Is that correct?

Spoiler

Why did you find for

s^2

?

s

is the displacement, not

s^2

I got

a = \dfrac{d^2s}{dt^2} = \dfrac{-6t(t^2 - 9)^2 + 12t(t^2 - 9) - 30t^2}{(t^2 - 9)^\frac{7}{2}}

(edited 9 years ago)

Original post by Khallil

I think ChemBoss meant the squares of sine of cosine!

Why can't you use double angle?

\cos (2x) = 1 - 2 \sin ^2 (x) \implies \sin ^2 (x) = \dfrac{1 - \cos (2x)}{2}

which can be differentiated using standard techniques¿¿¿

(edited 9 years ago)

Original post by Arithmeticae

...

Ah, you meant that! :frown:

:frown:

You're right of course!

It's been a long day, full of Physics :yawn:

:yawn:

Original post by Arieisit

...

This is what I got :s-smilie:

:s-smilie:

Spoiler

(edited 9 years ago)

Hello guys I know you all seem busy, I study medicine at uni but I have started doing maths in my spare time.

Can someone help me solve this simple one I keep getting the wrong answer

Original post by doctorteeth

...

Any maths is good practice for maths exams. Fire away!

Help with the question highlighted in pink .Just can get it to simplify -.- ImageUploadedByStudent Room1402775672.582730.jpg

ImageUploadedByStudent Room1402775672.582730.jpg

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