How good is your Mathematics?

**Brown, Jon Brow** · 9th Dec 06, 16:21

What do you get when you differentiate y=3a+5b(squared)

**imull** · 9th Dec 06, 16:25

y=3+10b

i think. worrying how much i have forgotten since i finished uni lol

**Brown, Jon Brow** · 9th Dec 06, 16:26

Yep, i hope

**Alfa Fan** · 9th Dec 06, 16:29

Just done A levels maths, so its pretty good

The expression you gave, has 2 variables in it a & b, therefore you would need to inform us what you want to differentiate with respect too.

However, I believe you mean to differentiate the fuction y = 5x2 + 3x

In which case the differential, dy/dx = 10x + 3

**EuroTroll** · 9th Dec 06, 16:29

Originally Posted by Brown, Jon Brow

What do you get when you differentiate y=3a+5b(squared)

Finally a thread to replace the geography one as the most popular!

I'd venture a guess that it's... oh, never mind.

**Brown, Jon Brow** · 9th Dec 06, 16:31

Originally Posted by Alfa Fan

Just done A levels maths, so its pretty good

The expression you gave, has 2 variables in it a & b, therefore you would need to inform us what you want to differentiate with respect too.

However, I believe you mean to differentiate the fuction y = 5x2 + 3x

In which case the differential, dy/dx = 10x + 3

Yeah I wanted dy/dx

**Alfa Fan** · 9th Dec 06, 16:31

Now we've solved that one, I'll post something a bit trickier.

y = 5x3 + 4x2 + 7

Give me the turning points of the function

**Brown, Jon Brow** · 9th Dec 06, 16:33

Is that where Y=0 ?

Diffrential of Y=0

**Alfa Fan** · 9th Dec 06, 16:40

You need to differentiate the funtion with respect to X. Then do what you suggested

The answer don't work out to exact decimals btw.

**Brown, Jon Brow** · 9th Dec 06, 16:50

Originally Posted by Alfa Fan

Now we've solved that one, I'll post something a bit trickier.

y = 5x3 + 4x2 + 7

Give me the turning points of the function

Is the equation y=5 multiplied by3 etc.....

or y=5cubed etc.....

**Alfa Fan** · 9th Dec 06, 16:53

cubed, you can't superscribe on the forum sadly.

**Brown, Jon Brow** · 9th Dec 06, 16:57

y=5xcubed+4xsqd+7

dy/dx= 5xsqd + 8x

at turning point dy/dx = 0
therefore 15x sqrd + 8x = 0

x(15 + 8) = 0

Turning points are (0,0) and (8/15,0)

**Alfa Fan** · 9th Dec 06, 17:01

points are (0,7) and (-8/15, 7.29)

You missed the effect of the +7 in the first one

**Brown, Jon Brow** · 9th Dec 06, 17:02

Originally Posted by Alfa Fan

Let me check - I might have made a mistake

looks like I need to do some revision before I do my Core 2 resit next month.

**Brown, Jon Brow** · 9th Dec 06, 17:05

(0,7) (8/15, 8.9)

**Alfa Fan** · 9th Dec 06, 17:07

Originally Posted by Brown, Jon Brow

looks like I need to do some revision before I do my Core 2 resit next month.

lol, good luck with that

Did that in June 2005 and got 70/100

**Alfa Fan** · 9th Dec 06, 17:11

Here's the working if you wondering where you've gone wrong...

y = 5x3 + 4x2 + 7

dy/dx = 15x2 + 8x

15x2 + 8x = 0

x(15x + 8) = 0

x = 0 15x + 8 = 0

x = 0 x = -8/15

When x=0

y = 5(0)3 + 4(0)2 + 7
y = 7

Therefore the first point is (0,7)

when x=-8/15

y = 5(-8/15)3 + 4(-8/15)2 + 7
y = 7.29.......

Therefore the second point is ~ (-8/15,7.29)