problem: Use the graphing strategy to sketch the graph of y=(4x)/(x^2+1). check the intervals where it is concave up and where it is concave down. Then graph it. please use sign charts.(adsbygoogle = window.adsbygoogle || []).push({});

to find this we have to first find y''.

so I used the quotient rule twice to get this

y'' = (8x^5 - 16x^3 - 24x)/(x^2 + 1)^4

to find the inflection points we set y'' = 0 and solve for x.

I have a question on this

while solving y'' = (8x^5 - 16x^3 - 24x)/(x^2 + 1)^4 = 0

i come across this step

(8x)(x^2 + 1)(x^2 - 3) = 0

so that would mean

8x = 0 this mean x = 0

(x^2 + 1) = 0 this means x = sqrt(-1)

(x^2 - 3) = 0 this means x = +-sqrt(3)

but do we just ignore the x = sqrt(-1) and conclude that the inflection points are x = 0, x = sqrt(3) and x = -sqrt(3)

So once we get the inflection points we use the sign charts to find concave up and concave down.

intervals where graph is concave up: (-sqrt(3), 0) & (sqrt(3), infinity)

intervals where graph is concave down: (-infinity, -sqrt(3)) & (0, sqrt(3))

are these intervals i found correct?

**Physics Forums | Science Articles, Homework Help, Discussion**

Dismiss Notice

Join Physics Forums Today!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Homework Help: Concave up and concave down

**Physics Forums | Science Articles, Homework Help, Discussion**