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**1. Homework Statement**

Solve the differential equation.

dy/dx = 4x + 4x/square root of (16-x^2)

**2. Homework Equations**

Substituting using U...

**3. The Attempt at a Solution**

I'm not sure if that's what I am supposed to do, but I tried using the U substitution...

4x + 4x/square root of (16-x^2)

u = 16 - x^2

du = -2x

-2du = 4x (I multiplied both sides by 2 and brought the negative over)

-2 (integration sign [the S]) du + du/square root of u

Take the anti-derivative...

-2 x (u)^(-1/2) + C (changed square root into a power)

-2 x (16-x^2) + C

Unfortunately, that is not the answer they give me. I'm kinda stuck.. am I going in the right direction?