i,
$y'=\dfrac{(1-\tan3x)'}{2\sqrt{1-\tan3x}}=\dfrac{-\dfrac{3}{\cos^23x} }{2\sqrt{1-\tan3x}}=\dfrac{-3}{2\cos^23x.\sqrt{1-\tan3x}}$
j,
$y'=\dfrac{(1+\cot2x)'}{2\sqrt{1+\cot2x}}=\dfrac{\dfrac{-2}{\sin^22x}}{ 2\sqrt{1+\cot2x}}=\dfrac{-1}{\sin^22x\sqrt{1+\cot2x}}$
k,
$y'=3(6x+\cos3x)^2.(6x+\cos3x)'=3(6x+\cos3x)^2.(6-3\sin3x)$
l,
$y'=10(x^2-1)^9.(x^2-1)'=10(x^2-1)^9.(2x)=20x(x^2-1)^9$
