Linear interpolation

Can someone help with this one, not sure which triangles i should be forming:

http://filestore.aqa.org.uk/subjects/AQA-MFP1-W-QP-JAN09.PDF

question 7

I'm thinking that i am wrong with c/d = b-r / r-a

Reply 1

lizard54142

6

Original post by Discutimos

Can someone help with this one, not sure which triangles i should be forming:

http://filestore.aqa.org.uk/subjects/AQA-MFP1-W-QP-JAN09.PDF

question 7

I'm thinking that i am wrong with c/d = b-r / r-a

PQ is a straight line, so has a constant gradient. Hence the gradient from (a,c) to (r,0) is the same as from (a,c) to (b,d). You can form two equations for the gradient, and then equate them.

Reply 2

Discutimos

OP

1

Original post by lizard54142

PQ is a straight line, so has a constant gradient. Hence the gradient from (a,c) to (r,0) is the same as from (a,c) to (b,d). You can form two equations for the gradient, and then equate them.

Ah.

so, c/(r-a) = d/(b-r) ?

EDIT:

Nope, (c-d)/(b-a) = c/(r-a) rearrange and boom

(edited 8 years ago)

Reply 3

lizard54142

6

Original post by Discutimos

Ah.

so, c/(r-a) = d/(b-r) ?

Looks fine to me. It might be easier if you find an expression for the gradient not in terms of r, i.e. from (a,c) to (b,d), so you don't have to do a lot of rearranging, but it doesn't really matter.

EDIT: You were one step ahead :wink:

Reply 4

Discutimos

OP

1

Original post by lizard54142

Looks fine to me. It might be easier if you find an expression for the gradient not in terms of r, i.e. from (a,c) to (b,d), so you don't have to do a lot of rearranging, but it doesn't really matter.

Yeah i suppose XD, finished the question now. Cheers.

EDIT: Cheeky :wink:

(edited 8 years ago)

Linear interpolation

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