# DIFFERENTIATION PRACTICE QUESTIONS WITH ANSWERS

Find the derivatives of the following functions with respect to corresponding independent variables :

Question 1 :

Differentiate f(x) = x - 3 sinx

Solution :

f(x) = x - 3 sinx

f'(x)  =  1 - 3 cos x

Question 2 :

Differentiate y = sin x + cos x

Solution :

f(x) = sin x + cos x

f'(x)  =  cos x - sin x

Question 3 :

Differentiate f(x) = x sin x

Solution :

f(x) = x sin x

We have to use the product rule to find the derivative.

u  =  x ==>  u'  =  1

v  =  sin x ==>  v'  =  cos x

Product rule :

d(uv)  =  uv' + vu'

f'(x)  =  x(cos x) + sin x (1)

f'(x)  =  x cos x + sin x

Question 4 :

Differentiate y = cos x - 2 tan x

Solution :

f(x)  =  cos x - 2 tan x

f'(x)  =  -sin x - 2 sec2 x

Question 5 :

Differentiate g(t) = t3cos t

Solution :

We have to use the product rule to find the derivative.

u  =  t3 ==>  u'  =  3t2

v  =  cos t ==>  v'  =  -sin t

f('x)  =  t3(-sin t) + cos t (3t2)

f('x)  =  -t3sin t + 3t2cos t

=  t2 (3 cos t - t sin t)

Question 6 :

Differentiate g(t) = 4 sec t + tan t

Solution :

g(t) = 4 sec t + tan t

g'(t)  =  4 sec t tan t + sec2 t

Question 7 :

Differentiate y = ex sin x

Solution :

y = ex sin x

u = ex  ===> u'  =  ex

v = sin x ===> v'  =  cos x

y'  =  ex (cos x) + sin x(ex)

y' =  ex (cos x + sin x)

Question 8 :

Differentiate y  =  tan x / x

Solution :

y  =  tan x / x

u = tan x  ===> u'  =  sec2

v = x ===> v'  =  1

Quotient rule :

d(u/v)  =  (vu' - uv') / v2

dy/dx  =  (x sec2 x  - tan x (1)) / x2

=  (x sec2 x  - tan x) / x2

Question 9 :

Differentiate y  =  sin x / (1 + cos x)

Solution :

y  =  sin x / (1 + cos x)

u = sin x ===> u'  =  cos x

v = (1 + cos x) ===> v'  =  - sin x

Quotient rule :

d(u/v)  =  (vu' - uv') / v2

dy/dx  =  ((1 + cos x) cos x - sin x (-sin x)) / (1 + cos x)2

dy/dx  =  (cos x + cos2 x + sin2 x) / (1 + cos x)2

dy/dx  =  (1 + cos x) / (1 + cos x)2

dy/dx  =  1/(1 + cos x)

Question 10 :

Differentiate y  =  x / (sin x + cos x)

Solution :

y  =  x / (sin x + cos x)

u = x ===> u'  =  1

v = (sin x + cos x) ===> v'  =  cos x - sin x

dy/dx  =  [(sinx+cosx) (1)-x(cosx-sinx)]/(sin x+cosx)2

dy/dx  =  [sinx + cosx - x cosx + xsinx)]/(sin x+cosx)2

dy/dx  =  [(1 + x) sinx + (1 - x) cosx]/(sin x+cosx)2

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