lim(x→0){(2x-sin2x)/(x*sin^2x)}
= lim(x→0){(2x-sin2x)/(x*x^2*(sin^2x/x^2))}
= lim(x→0){(2x-sin2x)/(x*x^2) * lim(x→0){(sin^2x/x^2)}
= lim(x→0){(2-2cos2x)/(3x^2)
= lim(x→0){(4sin2x)/(6x)
= lim(x→0){(8cos2x)/(6)
= 4/3