How do you find the linearization of f(x)=x^(3/4) at x=1?

1 Answer
Aug 1, 2016

I found: y=3/4x+1/4

Explanation:

Here we need to locally substitute the actual curve of our function with the line tangent to our curve at point of coordinate x=1.

Basically instead of considering the real curve we substitute it with a straight line (the tangent). This works locally, i.e., in a very small interval around our point so we must be careful not to overdo it!

We will need the equation of the line in the general form:
y-y_0=m(x-x_0)
where:
m is the slope;
x_0,y_0 are the coordinates of the point of interest.
In our case we have:
x_0=1 (given)
substituting into our function we see that: f(1)=y_0=1
Now we need the slope m; we can find it by deriving our function and evaluating it at x=1:
f'(x)=3/4x^(3/4-1)=3/4x^(-1/4)
evaluated at x=1:
f'(1)=m=3/4

Now we use: y-y_0=m(x-x_0) to get:
y-1=3/4(x-1)
or
y=3/4x-3/4+1
y=3/4x+1/4

Graphically:
enter image source here

You can see that around x=1 the line and the curve are almost the same thing, so, if you need, you can study the line instead of the original curve (where the curve may represent a phenomenon or tendency)!