Determine the interval on which the given function  f(x)= 3/10 x^4 - 4/5 x^3 - 3x^2 + 36/5 x + 11 
is (a).strictly increasing (b). strictly decreasing  

Asked by Deepak Singh | 6th Jan, 2016, 09:47: PM

Expert Answer:

begin mathsize 14px style f left parenthesis x right parenthesis equals 3 over 10 x to the power of 4 minus 4 over 5 x cubed minus 3 x squared plus 36 over 5 x plus 11 rightwards double arrow f apostrophe left parenthesis x right parenthesis equals 3 over 10 left parenthesis 4 x cubed right parenthesis minus 4 over 5 left parenthesis 3 x squared right parenthesis minus 3 left parenthesis 2 x right parenthesis plus 36 over 5 equals 6 over 5 x cubed minus 12 over 5 x squared minus 6 x plus 36 over 5 equals 6 over 5 open parentheses x cubed minus 2 x squared minus 5 x plus 6 close parentheses equals 6 over 5 left parenthesis x minus 1 right parenthesis left parenthesis x plus 2 right parenthesis left parenthesis x minus 3 right parenthesis end style

Answered by Rashmi Khot | 7th Jan, 2016, 12:11: PM

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