Quiz:Product rule for differentiation: Difference between revisions
No edit summary |
|||
| Line 43: | Line 43: | ||
+ If <math>f</math> and <math>g</math> are both differentiable at <math>x_0</math>, so is <math>f \cdot g</math>. However, differentiability of <math>f \cdot g</math> and <math>f</math> does not guarantee differentiability of <math>g</math>, and differentiability of <math>f \cdot g</math> and <math>g</math> does not guarantee differentiability of <math>f</math>. | + If <math>f</math> and <math>g</math> are both differentiable at <math>x_0</math>, so is <math>f \cdot g</math>. However, differentiability of <math>f \cdot g</math> and <math>f</math> does not guarantee differentiability of <math>g</math>, and differentiability of <math>f \cdot g</math> and <math>g</math> does not guarantee differentiability of <math>f</math>. | ||
- We cannot draw any inferences about differentiability of one of the three functions based on differentiability of the other two. | - We cannot draw any inferences about differentiability of one of the three functions based on differentiability of the other two. | ||
{Suppose <math>\mathcal{F}</math> is a collection of differentiable functions defined on all of <math>\R</math>. Further, suppose that there is a collection <math>\mathcal{B}</math> of functions such that every element of <math>\mathcal{F}</math> can be written as a polynomial in terms of the elements of <math>\mathcal{B}</math>, with constant coefficients. Suppose that the derivative of every element of <math>\mathcal{B}</math> is in <math>\mathcal{F}</math>. Which of the following conditions are sufficient to ensure that the derivative of every element of <math>\mathcal{F}</math> is in <math>\mathcal{F}</math>. | |||
|type="()"} | |||
- It is sufficient to ensure that <math>\mathcal{F}</math> is closed under addition and scalar multiplication, i.e., it forms a [[vector space]] of functions. | |||
- It is sufficient to ensure that <math>\mathcal{F}</math> is closed under multiplication, i.e., the product of any two elements of <math>\mathcal{F}</math> is in <math>\mathcal{F}</math>. | |||
+ It is sufficient to ensure that <math>\mathcal{F}</math> is closed under addition-cum-scalar multiplication (i.e., it forms a vector space), ''and'' closed under multiplication, but just having one of those conditions need not suffice. | |||
- It is not sufficient to ensure that <math>\mathcal{F}</math> is closed under addition-cum-scalar multiplication (i.e., it forms a vector space), ''and'' closed under multiplication | |||
</quiz> | </quiz> | ||
Revision as of 21:17, 5 December 2011
For a quiz that tests all the differentiation rules together, see Quiz:Differentiation rules.
For background, see product rule for differentiation and product rule for higher derivatives.
Formulas
Qualitative and existential significance
Computational feasibility
Computational results