[jameslad]

OCR Jun 10, Q8iii)

Here's the full question

i) express 2x^2 + 5x in the form 2(x+p)^2 + q

Answer: 2(x+ 5/4)^2 - 25/8

ii) State coords of the minimum points

(-5/4,-25/8)

PART THREE) State the equation of the normal to the curve at its minimum point..

So we know x coord of the minimum point is -5/4

How do work out the equation of normal? ( I know it should work out to be -1) so i assume the answer is 4/5? I dunno what am doing :P

..

Can you kindly guide me and if you do know the answer, can you tell me how you worked it Out

Thanks

[dongonaeatu]

equation of normal
is the perpendicular gradient of your tangent

and then you just slot the numbers in the formula y-y1-m(x-x1) where m is the gradient

[jameslad]

(Original post by dongonaeatu)
equation of normal
is the perpendicular gradient of your tangent

and then you just slot the numbers in the formula y-y1-m(x-x1) where m is the gradient

All that for one mark? I doubt that lol!

Must be something else

[dongonaeatu]

(Original post by jameslad)
OCR Jun 10, Q8iii)

Here's the full question

i) express 2x^2 + 5x in the form 2(x+p)^2 + q

Answer: 2(x+ 5/4)^2 - 25/8

ii) State coords of the minimum points

(-5/4,-25/8)

PART THREE) State the equation of the normal to the curve at its minimum point..

So we know x coord of the minimum point is -5/4

How do work out the equation of normal? ( I know it should work out to be -1) so i assume the answer is 4/5? I dunno what am doing :P

..

Can you kindly guide me and if you do know the answer, can you tell me how you worked it Out

Thanks

so you want to find out a gradient and you have
(-5/4,-25/8)
so y2-y1/x2-x1 gives you the gradient of the tangent

you want the gradient of the normal which is perpendicular

can you do this

[dongonaeatu]

(Original post by jameslad)
All that for one mark? I doubt that lol!

Must be something else

well the gradient of the normal is perpendicular to the gradient of the tangent

so if the gradient of a tangent is 2, gradient of the normal is -1/2

[raheem94]

(Original post by jameslad)
OCR Jun 10, Q8iii)

Here's the full question

i) express 2x^2 + 5x in the form 2(x+p)^2 + q

Answer: 2(x+ 5/4)^2 - 25/8

ii) State coords of the minimum points

(-5/4,-25/8)

PART THREE) State the equation of the normal to the curve at its minimum point..

So we know x coord of the minimum point is -5/4

How do work out the equation of normal? ( I know it should work out to be -1) so i assume the answer is 4/5? I dunno what am doing :P

..

Can you kindly guide me and if you do know the answer, can you tell me how you worked it Out

Thanks

is the minimum point, see the graph, from the graph we can see that the equation of the normal will be

[darkshadow1111]

isnt it just y=-25/8

[4mar_ar5en4l]

The gradient at the minimum point is 0, is it not.

Use that OP.

[darkshadow1111]

(Original post by raheem94)
is the minimum point, see the graph, from the graph we can see that the equation of the normal will be

wont that be the normal?
oh sorry just notice the question asked for the normal

[Intriguing Alias]

(Original post by jameslad)
OCR Jun 10, Q8iii)

Here's the full question

i) express 2x^2 + 5x in the form 2(x+p)^2 + q

Answer: 2(x+ 5/4)^2 - 25/8

ii) State coords of the minimum points

(-5/4,-25/8)

PART THREE) State the equation of the normal to the curve at its minimum point..

So we know x coord of the minimum point is -5/4

How do work out the equation of normal? ( I know it should work out to be -1) so i assume the answer is 4/5? I dunno what am doing :P

..

Can you kindly guide me and if you do know the answer, can you tell me how you worked it Out

Thanks

Well the normal is the perpendicular to the tangent.

If it's a minimum point - what is the gradient of the tangent ALWAYS?

[jameslad]

(Original post by raheem94)
is the minimum point, see the graph, from the graph we can see that the equation of the tangent will be

Equation of tangent? It's asking for normal..

[RebeccaTenney]

isn't it just x=-5/4?

[jameslad]

zero?

[Intriguing Alias]

(Original post by jameslad)
Equation of tangent? It's asking for normal..

He meant normal.

[raheem94]

(Original post by jameslad)
Equation of tangent? It's asking for normal..

By mistake wrote tangent, i have corrected it.

Sorry for the confusion it caused.

[jameslad]

That is the answer, but i'm just wondering .. why

[dongonaeatu]

(Original post by hassi94)
Well the normal is the perpendicular to the tangent.

If it's a minimum point - what is the gradient of the tangent ALWAYS?

minimum point- the gradient is positive is this right

[Intriguing Alias]

(Original post by jameslad)
zero?

Yes that's right so the tangent is just the horizontal line going through that point. Therefore the normal is the vertical line going through that point i.e. x = -5/4

[raheem94]

(Original post by dongonaeatu)
so you want to find out a gradient and you have
(-5/4,-25/8)
so y2-y1/x2-x1 gives you the gradient of the tangent

you want the gradient of the normal which is perpendicular

can you do this

The gradient of the tangent is zero.

So for finding the gradient of the normal will we do

We can't do this here!

[Intriguing Alias]

(Original post by dongonaeatu)
minimum point- the gradient is positive is this right

No. How do we find minimum points using calculus?