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## Homework Statement

the question asked to prove that the double derivaitve of y=tan(x) is...

2y(1+y^2)

eg. 2tanx(1+tan^2(x))

## Homework Equations

## The Attempt at a Solution

I was able to get the first derivative ( i think)

y=tan(x)

=(sin(x))/(cos(x))

dy/dx=(cos(x)cos(x)-(sin(x)(-sin(x))))/cos^2(x)

=(cos^2(x)+sin^2(x))/cos^2(x)

=1/cos^2(x)

from here i am not to sure how to get the second derivative...