Precalculus question. if f(x) = 3x + 7, find [ f (a + h) - f (a) ] / h?

Original post by notnek

This is "differentiation from first principles" which is not simple so I doubt anyone is going to give you a full explanation here.

I recommend you look in a textbook or search Google for an explanation.

Challenge accepted! :P

Reply 3

Original post by finewhateverx

Precalculus question. if f(x) = 3x + 7, find [ f (a + h) - f (a) ] / h?
what brings a and h into all of this?? v confused as i havent done this stuff in a while.

To find f(a + h) you substitute (a + h) for x into f(x).

Reply 4

OP

Original post by notnek

This is "differentiation from first principles" which is not simple so I doubt anyone is going to give you a full explanation here.

I recommend you look in a textbook or search Google for an explanation.

thank you i'll look that up

Reply 5

OP

Original post by Muttley79

To find f(a + h) you substitute (a + h) for x into f(x).

sorry but could you explain why?

Reply 6

Original post by notnek

This is "differentiation from first principles" which is not simple so I doubt anyone is going to give you a full explanation here.

I recommend you look in a textbook or search Google for an explanation.

never mind, they haven't even learnt f(x) notation, you were right :frown:

Reply 7

Original post by finewhateverx

sorry but could you explain why?

Have you met function notation?

For example if f(x) = 5x + 3 then f(2) = (5 x 2) + 3 = 13

Reply 8

Original post by Muttley79

Have you met function notation?

For example if f(x) = 5x + 3 then f(2) = (5 x 2) + 3 = 13

or, more clearly:

Unparseable latex formula:

f(x) = 2x^2 + 4x + 7\[br]\[br][br]f(3) = 2(3)^2+4(3) + 7 = 37\[br]f(5) = 2(5)^2+4(5) + 7 = 77\[br]

Reply 9

Original post by Callum Scott

or, more clearly:

Unparseable latex formula:

f(x) = 2x^2 + 4x + 7\[br]\[br][br]f(3) = 2(3)^2+4(3) + 7 = 37\[br]f(5) = 2(5)^2+4(5) + 7 = 77\[br]

That's NOT clearer - the function the OP is dealing with is linear - you've just over-complicated it!

Reply 10

Original post by Muttley79

That's NOT clearer - the function the OP is dealing with is linear - you've just over-complicated it!

the function is more complicated, but the idea it conveys is much clearer with more terms, and the LaTex format.

Reply 11

OP

Original post by Muttley79

Have you met function notation?

For example if f(x) = 5x + 3 then f(2) = (5 x 2) + 3 = 13

yes i am aware of that but
how can i conclude from the question that i have to substitute (a+h) for x?
if f(x) = 3x + 7, find [ f (a + h) - f (a) ] / h?
i don't see what brings a and h into all this. sorry it's probably really simple but its been a while and i just can't make anything of it

Reply 12

Notnek

21

Original post by Muttley79

That's NOT clearer - the function the OP is dealing with is linear - you've just over-complicated it!

If the OP can't deal with quadratic functions then I doubt they'll be able to handle differentiation from first principles :smile:

Reply 13

OP

Original post by notnek

If the OP can't deal with quadratic functions then I doubt they'll be able to handle differentiation from first principles :smile:

guys id appreciate it if youd stop being so condescending and help out, or else please leave. for background im done with alevels and in my second yr of med school havent done maths for two years, had to do an Aelective precalculus course, came across this question which for some reason or other i cant seem to be able to make head or tail of. if you can clarify things then please do so and if you cant then honestly whats the point of hanging around?

Reply 14

Original post by Callum Scott

the function is more complicated, but the idea it conveys is much clearer with more terms, and the LaTex format.

Don't overcomplicate a simple idea.

Reply 15

Original post by finewhateverx

guys id appreciate it if youd stop being so condescending and help out, or else please leave. for background im done with alevels and in my second yr of med school havent done maths for two years, had to do an Aelective precalculus course, came across this question which for some reason or other i cant seem to be able to make head or tail of. if you can clarify things then please do so and if you cant then honestly whats the point of hanging around?

I am trying to help - I can't help idiots showing off.

When you have anything in function notation then that means replace x by whatever is in the bracket - that how function notation is defined.

(edited 8 years ago)

Reply 16

Original post by finewhateverx

guys id appreciate it if youd stop being so condescending and help out, or else please leave. for background im done with alevels and in my second yr of med school havent done maths for two years, had to do an Aelective precalculus course, came across this question which for some reason or other i cant seem to be able to make head or tail of. if you can clarify things then please do so and if you cant then honestly whats the point of hanging around?

That was being condescending to the person he was replying to :awesome:

, not you lol :P

Reply 17

Notnek

21

Original post by finewhateverx

guys id appreciate it if youd stop being so condescending and help out, or else please leave. for background im done with alevels and in my second yr of med school havent done maths for two years, had to do an Aelective precalculus course, came across this question which for some reason or other i cant seem to be able to make head or tail of. if you can clarify things then please do so and if you cant then honestly whats the point of hanging around?

I can see how my comment seemed like it was directed at you but it wasn't. I was making a point to Muttley79.

I'd be the last person to put someone down based on their mathematical knowledge.

Reply 18