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Brief Calculus Review
Functions
A function is a relationship between 2 or more variables. For example, we might say that the variable Y is related to the variable X as follows:
We call X the independent variable and Y the dependent variable.
Thus, when X takes the value of 1 Y is 1, when X is 2 Y is 4 and so on.
By taking the square root in both sides we can invert this function as follows.
Thus, when Y takes a value of 4, X equals 2, when Y takes a value of 1 X equals____
Rules of differentiation
Broadly speaking, the rules of differentiation help us answer this question: if the independent variable changes by one unit, how much will be the change in the dependent variable.
Suppose we have the following function,
If we increase X by one unit, how much will Y change? Let’s pick some numbers. Suppose first that X is 10. This implies that Y is 10x2 or 20. Now we increase X by one unit to 11. Then Y equals 11x2 or 22. Thus the change is 2. If we increase X from 11 to 12? Y equals 24, which means that the change in Y equals 2.
We have the following result,
Suppose we have,
where A is any positive or negative number (in the previous example A=2), the derivative of Y with respect to X (the change in Y for a one unit change in X), which we write as is
Constants
Suppose instead that the function is
where B and A are any positive or negative constants (numbers). How does Y change? Since B is a constant, when X changes the result will be the same as before (try by picking some numbers for X and Y). That is, the derivative of a constant is zero.
Power rule
Now suppose we have a function that looks like this
where A and b can be any positive or negative number.
How does Y change if X increases by one unit?
The rule is
For example let the function be,
, then
Now let’s combine two things (a constant multiplying a power variable)
the derivative of Y with respect to X is,
Product rule
Suppose we have two...