Parametric equations

Probs a result of doing papers at night running on pure caffeine but

x^2 + 4xy + 2y^2 + 18 = 0

how do I eliminate x or y😓

(the question is to find stationary points on the thing and I'm basically solving 2x+4y=0 after differentiating)

cheers

Reply 1

Notnek

21

Original post by okcherubble88

Probs a result of doing papers at night running on pure caffeine but

x^2 + 4xy + 2y^2 + 18 = 0

how do I eliminate x or y😓

(the question is to find stationary points on the thing and I'm basically solving 2x+4y=0 after differentiating)

cheers

How are parametric equations involved? Can you post the question in full?

And can you also post your full working.

Reply 2

Kevin De Bruyne

21

Original post by okcherubble88

Probs a result of doing papers at night running on pure caffeine but

x^2 + 4xy + 2y^2 + 18 = 0

how do I eliminate x or y

(the question is to find stationary points on the thing and I'm basically solving 2x+4y=0 after differentiating)

cheers

You have two equations and two unknowns.

Reply 3

ChoccyPhilly

13

Original post by okcherubble88

Probs a result of doing papers at night running on pure caffeine but

x^2 + 4xy + 2y^2 + 18 = 0

how do I eliminate x or y😓

(the question is to find stationary points on the thing and I'm basically solving 2x+4y=0 after differentiating)

cheers

That would be implicit differentiation. When you differentiate y in dy/dx you differentiate as normal but leave a multiple of dy/dx. For the 4xy, you use the product rule with implicit differentiation.

Reply 4

okcherubble88

OP

9

fml
even got the wrong name
god help me

Q) Find the stationary points on the above curve
Differentiated to dy/dx = -4y-2x / (4x+4y)
stationary points needed so 2x+4y =0
But don't know/forgotten how to solve that

Reply 5

okcherubble88

OP

9

Ohh I'll solve them simultaneously I see

Thanks!

A* material right here

Reply 6

lydia136

don't feel bad, earlier today while doing a C4 paper i did 1.5-1 on my calculator and i am predicted A* at a level! &caffeine is the only thing getting me through revision lol