realize that #1 - cos^2 x = sin^2 x # due to the trigonometric identity # sin^2 x + cos^2 x = 1 #

therefore the top equation becomes #sin(x) * x^2 * sin(x)# which is equal to #x^2 * sin^2 (x)#, after removing the common factors #x^2# of the denominator and the numerator, you are left with #sin^2 (x) / x^4#

the #sin^2# function has its domain over only 1 and 0 so it will never be negative or more than that and the bottom function #x^4# gets smaller and smaller as #x# approaches #0#, so the top function which is a number between 0 and 1 is divided by an increasingly small number, so the limit of the whole function as #x# approaches 0 is positive Infinity