How do you differentiate #log_2(x^2sinx^2) #?

1 Answer
Jun 26, 2016

#= 2/(ln 2) ( 1/x + x cot x^2)#

Explanation:

#(log_2(x^2sinx^2))'#

first we need to shift the base into natural logs as these are just made for calculus

so using #log_a b = (log_c b)/(log_c a)#

so
#log_2(x^2sinx^2) = (ln (x^2sinx^2))/(ln 2) = 1/(ln 2)ln (x^2sinx^2)#

then we use another standard result namely that

#(ln f(x))' = 1/(f(x))*f'(x)#

so #( 1/(ln 2)ln (x^2sinx^2))' = 1/(ln 2)( ln (x^2sinx^2))' #

#= 1/(ln 2)1/ (x^2sinx^2) (x^2sinx^2)' \\qquad square#

for # (x^2sinx^2)'# we use the product rule

# (x^2sinx^2)' = (x^2)'sinx^2 + x^2 (sinx^2)' #

#= 2x sinx^2 + x^2 (sinx^2)' \qquad star#

for #(sinx^2)'# we use the chain rule so

#(sinx^2)' = cos x^2 (2x) = 2x cos x^2#

pop that back into #star # to get

# (x^2sinx^2)' = 2x sinx^2 + x^2 * 2x cos x^2 #
#\implies (x^2sinx^2)' = 2x sinx^2 + 2x^3 cos x^2 #

pop that back into #square# for

#( 1/(ln 2)ln (x^2sinx^2))' = 1/(ln 2)1/ (x^2sinx^2) (x^2sinx^2)'#

#= 1/(ln 2)1/ (x^2sinx^2) (2x sinx^2 + 2x^3 cos x^2)#

this can be simplified in any number of ways, so i'm going for brevity

#= 2/(ln 2) ( 1/x + x cot x^2)#