# Interactive video lesson plan for: unit 3 test corrections 7 Derivative of absolute value functions

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Right let's take a look at question number seven we are to find F prime if F is the absolute value of three X plus two okay so there two possible solutions you can have for this the derivative of this function so the first one I'm going to be using the differentiation rule DDX of the absolute value you equals you over the absolute value you the you the X okay this is one possibly of finding the derivative of this function okay so solution one were going to be using this formula right here we also going to be applying the chain rule okay this is a composition of two functions is a composition of the absolute value function and the linear function okay so we have all F F of G of X equals the absolute value of three X plus two okay and we know what the chain rule is right so one of find the derivative of F of G of X so F of G of X prime is equal to F prime of G of X the derivative of the outer function and I evaluated at the inner function times the derivative of the inner function so we are going to apply the chain rule here so let's see what the have we have all the compose this composite function take out F F of X is the absolute value X that is the outer function now the inner function is G of X G of X is of three X plus two okay now is going to proceed to find the derivative of these two functions now the derivative of F F prime of X is X over the absolute value of X the derivative of G G prime of X is three so what we going to do is find F prime of X and I waited at G so we just simply take G and plug it into the X is the F prime of X okay and then multiply it by G prime of X so F prime of X is simply going to be F prime of G of X is instead of X divided by the absolute value X within a have three X is to taking the place of X so have three X plus two divided by the absolute value three X plus two using the chain rule formula we are to multiply this result by the derivative of the inner function G prime of X okay so of G prime of X is three so just multiply this by three so that's your answer okay we can simplify into F prime of X equals nine X plus six divided by the absolute value of three X plus two so there is your first solution now the second solution that we going to generate involves expressing this function is piecewise be find function okay on this result is also equally correct so solution to solution to we're going to write the absolute value function as follows this is going to be we know that F of X which equals the absolute value three X this to can be written as plus or minus three X plus two the sign change happens when the argument of the absolute value function changes sign okay so we just have to so three X was to equals zero so this four X and that will tell you where you sign change happens okay so we subtract two and divide by three we have X equals negative two thirds prime so now all function is negative three X plus two when X is less than negative two thirds and three X plus two when X is greater than or equal to two negative two thirds okay so now this is our piece wise find function now what were going to do is find the derivative of this piecewise be find function so F prime of X is simply going to be the derivative of the function to the left which is negative three X plus two the derivative of that is negative T three when X is less than negative to third and this on the bottom is three when X is going to then or equal to negative to third okay so this is another possible solution for the derivative of the absolute value of three X plus two okay so any of these solutions you will get for credit you have to find the derivative of these absolute value function thanks so much for taking the time to watch this presentation really appreciated feel free to subscribe to our channel for updates to other cool tutorials such as this and also feel free to post a comments in the comments section to let us know what you think about this lesson more clips can be, mathgotserved.com thanks again for watching and have a wonderful day

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