Posted: Feb 17, 2012 9:56 am
CONSTANTS AND POWERS
Now, since we understand a couple of basic things about differentiation, let's start seeing how to do it.
Rule #1: Any constant's derivative is equal to 0.
A constant is a definite quantity like 5, or 45 or maybe 567; so for example:
[math]
Its derivative (with respect to x), is:
[math]
You can change the constant to any value you wish; its derivative is still 0. And when in an equation you are told that a certain symbol is to be treated like a constant, then its derivative will be 0. For example:
[math]
And you are told that c is a constant by definition. Then the function will have derivative 0, since c is considered to be a constant (of unknown quantity).
[math]
More examples I will do more at the end of this post.
Rule #2: if you have a function like [math], then its derivative will be [math]
Let's take the parabola of my first post:
[math]
Notice that n=2; so n-1 = 1, and the resulting derivative will be:
[math]
One should always remember that [math]; there is no need to put the power of 1 to any variable or constant. Also we should remember that [math] no matter what the variable, quantity is.
So, if we have:
[math]
then n=1, so n-1 = 0, then the derivative of the above is [math].
Let's do a couple more examples:
[math]
So, we have n=19, and n-1 = 19-1 = 18, so its derivative will be [math]. How about the second derivative though? The rule is that when you have a constant before a power that constant remains unaffected in differentiating. When I will explain more complex functions like [math]or [math], you will see why this constant is not differentiated to 0. For the moment, just take it as part of the definition.
The definition then is amended to:
[math]
Its derivative will be:
[math]
So, if we want to make the second derivative of the above what happens?
[math]
We have a=19, n=18, n-1=17. So plugging in the numbers we have:
[math]
[math]
Another very important thing to remember is the following: if a function is made up of addition of other functions, then its derivative will be the addition of the derivatives of those functions.
In mathematical terms:
[math]
then the derivative will be:
[math]