Question

if f(x)=3-x^2, find f(2+delta x) .... i dont know how to do these problems using delta so please explain

Answer 1

wherever x is there in the function f(x)
to find f(2+delta x) replace x with 2 + delta x)
so the function for f(x) which was 3- x^2
becomes
3-(2+delta x)^2
now we expand this,
3-(2+delta x)(2+delta x)
=3-(2*2+2*(delta x)+ (delta x )* 2+(delta x)*(delta x))
=3-(4+4*(delta x)+(delta x)^2)
=-1-4(delta x)-(delta x)^2
If you assume (delta x to be small,i.e. (delta x) <<1 then we can neglect the (delta x)^2 term)

Answer 2

why do you have to assume that delta x is small?

Answer 3

Obviously u could get -1 from simply substituting 2 into f(x).

This is some sort of exercise (as a part of others, I would think) to show you how u may get to a result by showing how a small change in x leads to the same result.

Delta x need not be assumed to be small but delta x is traditionally taken to mean a small change in x.

Answer 4

oh ok thank you

Answer 5

U r welcome.