<p>x(9-4x)^-.5</p>
<p>how do you find this derivative. I think my teacher messed up the answer key which is confusing me.</p>
<p>OK, let’s take a stab at it…</p>
<p>Set u=x, v=(9-4x)^-0.5
Then du/dx = 1
dv/dx = (-0.5)(9-4x)^(-0.5 -1) * d(9-4x)/dx
= (-0.5)(9-4x)^(-1.5) * (-4)
= 2(9-4x)^(-1.5)</p>
<p>You need d(uv)/dx = uv’ + vu’
= x(2)(9-4x)^(-1.5) + ((9-4x)^-0.5)(1)
= ((9-4x)^-0.5) ( (2x / (9-4x)) + 1)</p>
<p>do you need to differentiate by parts? you can’t just use the product rule?</p>
<p>Optimizerdad DID use product rule…he just showed ALL of the steps. I got the same answer, FWIW.</p>
<p>…yeah, us old geezers tend to get <em>way</em> too detailed 
.</p>
<p>52 does not make you a “geezer”. Puh-Leeze. ;)</p>