find the open intervals on which the function ​f(x)axbx​c, a​0, is increasing and decreasing. describe the reasoning behind your answer.

Respuesta :

The intervals on which the function f(x) = ax² + bx + c (where "a" doesn't = 0) is increasing and decreasing is x>-b/2a and x<-b/2a

Given that,

We have to find the intervals on which the function f(x) = ax² + bx + c (where "a" doesn't = 0) is increasing and decreasing.

We know that,

Take the function equation,

f(x)=ax² + bx + c

The derivative of the function of x is  

f'(x)=ax+b

So, f(x) is increasing when f'(x) > 0

f(x) is decreasing when f'(x) < 0

Then we can say

f'(x) > 0 , when  b > 0  and a < 0

2ax + b < 0

2ax < - b

x<-b/2a

Now,

f'(x) < 0 , when  b < 0  and a > 0

2ax + b > 0

2ax > - b

x>-b/2a

Therefore, the intervals on which the function f(x) = ax² + bx + c (where "a" doesn't = 0) is increasing and decreasing is x>-b/2a and x<-b/2a.

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