What is k in your 'solution'? ...
What you have to do is taking the first derivative of f(x) and then let f'(x)=-1.
your equation has two unknowns, , and the y-intercept of the tangent line, . you need another equation ...
I have to ask since you posted this in the PreCalculus forum, do you know what this second equation means?
... if so, are you free to use the basic derivative rules, or are you required to find the derivative from first principles (the limit definition)?
I do have another question though. How did you get from: to
I do understand that the solution is the values of k where the discriminant is equal to 0.
I am having difficulties understanding the algebraic process in order to determine the discriminant.
I am doing this:
I get here and I am like, "OK, using the quadratic formula what terms in this equation are and so that I know how to set up the discriminant?" based on the commonly presented:
(just to clarify what i am saying)
It is clear to me that must be based on what you have presented. But how does one exactly know that?
Algebraically, what steps are you taking?
Thanks in advance.
Sincerely,
Raymond MacNeil
Actually, there are still some things I need to clarify if you don't mind. Why do you have:
?
Should it not be: ?
Would not give ?
**EDIT: OK algebraically I see how it makes sense, but how did you know your were suppose to make that modification to correctly solve for K?**
And, in your original post, why were you able to divide the discriminant by 4? I thought the discriminant was simply:
[A] I've made the experience that for me a leading factor a = -1 causes a lot of mistakes. So I usually divide through the equation by the leading factor such that a = 1. Then I don't have to think about it in the following calculations any more:
[B] That's a question of definition: I've learned that the discriminant is the term under the root-sign (in Germany such a term is called radicand) if it determines different solutions of an equation (dicriminare is a Latin word which means to separate, to put apart)
So in my opinion the discriminant could be:
... or ...