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# show function f(x) is decreasing

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138
3
+838

ok so for this question so far i have found out dy/dx

which is: 3- 20x^4 -15x^2

then im not sure how to show that as on the previous questions i was given a value to sub in.

thank you for the help.

Dec 17, 2018

### 3+0 Answers

#1
+5095
+2

$$f'(x) = -3 - 20x^4 - 15x^2\\ \text{this should pretty clearly be less than zero for all }x$$

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Dec 17, 2018
#2
+838
+1

oh right i forgot the - sign haha thank you for helping.

YEEEEEET  Dec 17, 2018
#3
+101046
+1

Before you ask more completely new questions take some time to digest what you have already been given.

Dec 17, 2018