1, the commonly used fraction (sinx 2-x 2)/(x * sinx 2 x * sinx 2), and then replace it with the equivalent infinitesimal.

Get [(x- 1/6 * x 3) 2-x 2]/x 3 = 0.

5. The numerator is just the derivative of the denominator, so the original formula = ln | x 3+2x2+2x+1|+c.