Parents of Year 11DC support thread. The final term.

[OhYouBadBadKitten]

Eep.

Dds school does AS too , though she's doing Maths which is still old style.

Surds and the surface area of cylinders. Shoot me now. I'd never even heard of a surd a month ago......

We had an attack of surds, Ds had it set as homework before the teacher had covered it. My A level maths and stats was a long time ago but google and the revision guide are my friends. Funnily enough when he came to revise surds DS had no problem at all remembering it. He is on his own with solid geometry as that wasn't on my syllabus but he doesn't have any problem with that. I am grateful for small mercies.

surds are lovely :) didnt used to be a 'thing' but there is a nice elegance to them.
Maths is the only thing I have a clue on.... apart from physics, but I have no idea what is in the curriculuum.

I have no idea of what surfs are! This is the first time I have ever heard of them presumably ds1 knows, I might ask him tomorrow
Dream, I only know what we were told by the officer recruiter at the career fair so I could be wrong or it may have changed. I am sure we will find out more info if ds1 decides its worth pursuing. He definitely said they choose the regiment after a year because my df is a vet and we discussed it in detail.

I surprised myself today by dredging from my memory the process of blood clotting that I learned for O level biology. Impressed child was impressed (and so was I).

Its using surds in finding the height of a cylinder, when you've been given the surface area. Dream - if your dd has the Jan paper 4h, maybe she can have a look and let me know!

if hes really stuck and desperate Derek, let me know. but he can use the mark scheme for a general guide.

(Derek* I haven't looked ta the paper, but this may help (or may not)

Surface Area of cylinder =

area of top and bottom PLUS area of curved surface
2 x pi x radius-squared PLUS 2 x pi x radius x height
so rearranging,
2 x pi x radius x height = Area - 2 x pi x radius-squared

height = (Area - 2 x pi x radius-squared)/(2 x pi x radius)

I don't really think there are any surds as such in sight for that.

Surface area is fine - on it's own...

Cylinder has a radius 4√3 & height h cm
Total area 56π√6²

Find exact value of h
Give your answer in the form a√2 + b√3 where a and b are integers

He has missed some maths lessons.....

assuming you mean area has sqrt(6) not sqrt(6-squared).

OK. Plug into the formula, and simplify. All the pis disappear.

Is it because he ends up with a sqrt(3) on the bottom?

Then multiply top and bottom by srt(3)

A sqrt(6)xsqrt(3) = 3sqrt(2), I suspect that's what he doesn't know?

sqrt(6) x sqrt(3)

= sqrt(18)

= sqrt(9) x sqrt(2)

= 3 x sqrt(2)

Nope, more steps needed -baby steps please

Radius = 4√3

So area of a circle formula means Area of top is π x 4√3 x 4√3 = 16x3xπ = 48π
So area of top and bottom together is twice that so 96π

Area of curved bit is circumference of circle times height (imagine cutting a toilet roll and flattening it out
Area curved bit = 2 x π x 4√3 x height = 8π√3 x height

So 96π + heightx8π√3 = 56π√6

Divide everything by π

96 + heightx8√3 = 56√6

Divide everything by 8

12+height√3 = 7√6

rearrange

height√3 = 7√6 - 12

easiest now to multiply everything by √3

...tricky step 1 ... (√3 x √3 = 3)
heightx3 = 7√6√3 - 12√3

.... tricky step 2 ....(√6√3 = √18 = √9√2 = 3√2)
heightx3 = 7x3√2 - 12√3

now divide by 3

height = 7√2 - 4√3

So you need to know sqrt(ab) = sqrt(a) x sqrt(b)

And sqrt(a^2) = a

Q23 out of 25

Thanks t&t
I've copied it out - hopefully he'll feel up to looking at it later

Good stuff Tween.
If its not obvious to multiply throughby rt3 then divide by it, but remember to sort out the fraction at the end - fractions should never be left with surds in the denominators!

Depends what your target is Dream.