Need some help please guys, the wife is helping our niece revise for her gcse but we are struggling to remember these equations......

q1. for the equation, y=5000x - 625 xsquared, find dy/dx?

q2. find the co-ordinates of the turning point on the graph

y=5000x - 625 xsquared

Thanks

Leigh

 

Fuck knows.

 

Holy macaroni batman, WTF.

I think maybe you're over-estimating the intelligence levels on here.

 

Thanks

I just told my neice " we have a reply, dont panic"

Regards

leigh

 

+ 1 !!!!

 

Come on Leigh!


THINK its easy!














Think again its not

 

jeez, this takes me back, its about differentiation between expressions blah blah blah, give me a few mins to try and remember and i will get back to you

 

Come on Luke, you must remember this.......its been 20 years since I done 'o' level maths

There is a second question coming soon......

Leigh

 

Thanks mate, this question alone is worth nearly 5% of the whole gcse exam

Leigh

 

well what you do is y5000x multiple x squared divided by 5000yx = + -dy half it by dx= fuck noes

 

have you got a graphical calculator?

 

no mate, just scentific

Leigh

 

Wheres that Jimbo ???

Lets see if he fell asleep in this lesson

 

lol, i am going to have to remember how to do it properly then, i think i am getting there anyway, lol

p.s why the hell do kids need to know this?? lol

 

y = 5000x - 625x^2
First find dy/dx = 5000-1250x

Now there are turning points when dy/dx = 0, so:

0 = 5000 - 1250x
1250x = 5000
x = 500/125 or 4

To find the y-coordinate of the turning point, put this value of x into the original function:

y = 5000x - 625x^2
= 5000(500/125) - 625 (500/125)^2
=20000 - 10000
= 10000

So there is a turning point at (4, 10000)

I'm pretty sure this is right.
Rich

 

How do you jump to this..

First find dy/dx = 5000-1250x

????

Thanks

leigh

 

i am pretty sure you are right, that is the answer i got on my graphical calculator, i was just struggling, to work it back, lol

 

We are struggling with this part

____________

y = 5000x - 625x^2
First find dy/dx = 5000-1250x

Now there are turning points when dy/dx = 0, so:

0 = 5000 - 1250x
1250x = 5000
x = 500/125 or 4

_____________

We see that you have divided both sides by x, but should it not then be

5000-625x ??


Thanks

leigh

 

cheeky bastard

i just done my gcse's, well 10months ago, and got an A in maths

but this !! is way past me

 

Come on Jimbo, this is a past paper from 2006.....

Leigh

 

Y = 5000x – 625xsquared

First dy/dx = 0
So divide both side by x

y/x = (5000x / x) – (625x2/x) = 0

cancel the x’s out
0 = 5000 – 625x

Divide all parts by 625
0/625 = (5000/625) – (625x/625)

simplify
0 = 8 – x

Plus x to both sides

X = 8

No substitute x = 8 into original equation

Y = (5000 * 8) – (625 * 8)

Y = 40000 – 5000

Y = 35000

hope this helps

 

sry forgot to square 8 on last part of equation, here it is again

Y = 5000x – 625xsquared

First dy/dx = 0
So divide both side by x

y/x = (5000x / x) – (625x2/x) = 0

cancel the x’s out
0 = 5000 – 625x

Divide all parts by 625
0/625 = (5000/625) – (625x/625)

simplify
0 = 8 – x

Plus x to both sides

X = 8

No substitute x = 8 into original equation

Y = (5000 * 8) – (625 * 8squared)

Y = 40000 – 40000

Y = 0

 

Beat me too it.

 

Oh Leigh


Jimbo asked whens your neices Prom

 

We have sussed it out using half your answer and half sonic booms answers

No substitute x = 8 into original equation

Y = (5000 * 8) – (625 * 8)

Y = 40000 – 5000

Y = 35000

hope this helps

You forgot to square the 625 8x ^2

so

40000 - 625 x 64 =y

y = 40000 - 40000 =0

So are we correct in saying

x = 8

y = 0

 

i did repost it correctly just after my last post but not quick enough lol

 

Part 2

Is the turning point a max or a min?

Gut feeling its a min due to the negative value in the equation

Thanks for the help so far

Leigh

 

Just noticed mate, apologies, I have the wife and neice talking in my ear and I cant multi task!!!!

 

Thanks for your input Luke, you are clearly as good at maths as you are at launching your car of the line

Leigh

 

if Y is a positive value then its the minimum turning point, i think y = 0 is classed as a positive value but not 100%

 

What did I manage to balls up?
Rich

 

Yes 0 is a positive number
Rich

 

many thanks for the help guys

She is on her way home but is back tomorrow night as we have helped her so much

Stand by for the next installment tomorrow

Thanks

Leigh

 

Oh I seen my error I actually times it by 2. What a numpty!!!
Rich

 

there is no need, you have x on both side of the equation, so that leaves you with

5000 - 625^2, ie 5000 - 1250

 

but its 5000x - 625 x^2 (x squared)

so if you divide both sides by x then its

5000 - 625x

I think

Leigh

 

lol, i am doing the same thing, x2 instead of to the power of 2

 

shit no, you are right, its the x that is squared

 

I used to be really clever, Grade B in maths I got... But let me ask, WHAT THE HELL ARE YOU ALL ON ABOUT?

 

Christ, that totally re-affirms why I hate maths. What possible use is that stuff in the real world? Is there any time when you'd actually need to do something like that? (Serious question!)