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Assignment 13

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M102 - Mathematics II

Assignment 13

1. Let f (x) = cos (ax) for x ∈ R where a ̸= 0. Find f (n) (x) for n ∈ N, x ∈ R.

2. Let g(x) = |x3 | for x ∈ R. Find g ′ (x) and g ′′ (x) for x ∈ R and g ′′′ (x) for x ̸= 0. Show
that g ′′′ (0) does not exist.

3. Find the nth derivative of the following functions:

(a) x2 e3x sin 4x (c) x log x


ln x sin x
(b) (d)
x+1 1 + x2

4. If y = a cos log x + b sin log x, show that x2 y2n+2 + (2n + 1)xyn+1 + n(n + 1)yn = 0.

5. If y = log (x + 1 + x2 ). Prove that (1 + x2 )yn+2 + (2n + 1)xyn+1 + n2 yn = 0.

6. 
 xn sin 1 if x ̸= 0
Let f (x) = x
 0 if x = 0.
Then f (k) (0) exists for all k < n, but f (n) (0) does not exist.

7. Let m, n ∈ N. Consider the function


(
xn x > 0
f (x) =
xm x ≤ 0.

Discuss its high-order differentiability.

8. Determine whether or not x = 0 is a point of relative extremum of the following


functions:

(a) f (x) := x3 + 2 1
(c) h(x) := sin x + x3
6
1
(b) g(x) := sin x − x (d) k(x) := cos x − 1 + x2 .
2

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