So I've been trying to differentiate this one problem, and then solve when the derivative is equal to 2. The equation in question is sqrt[(5x+1)/(4x^2+1)

Now for my answer before plugging in two I got .5((((20x^2+5)-(40x^2+8x))/(16x^4+8x^2+1))^(-1/2)

however this is obviously not a correct calculation - what was I doing wrong?