What are the points of inflection of #f(x)=8x^2 + sin(2x-pi) # on # x in [0, 2pi]#?

1 Answer
Apr 30, 2018

None. No points of inflection.

Explanation:

Points of inflection are slope extrema or #f'(x)# extrema. To find a maximum or minimum, take the second derivative and set equal to zero, to find where change in slope is zero.

#f(x)=8x^2+sin(2x-pi)#
#f'(x)=16x + 2cos(2x-pi)#
#f''(x)=16 - 4sin(2x-pi)#

Now set #f''(x)=0#:

#0=16-4sin(2x-pi)#
#-16=-4sin(2x-pi)#
#4=sin(2x-pi)#
#sin^-1(4)=2x-pi#
#->#NO SOLUTION

There are no (real, I dunno about complex) solutions as sin(x) cannot be greater than 1.

Therefore there are no points of inflection.