Left Side: #=csc^4 theta - cot^4 theta#
#=1/sin^4 theta - cos^4 theta /sin^4 theta#
#=(1-cos^4 theta)/sin^4 theta#
#=((1+cos^2 theta)(1-cos^2 theta))/sin^4 theta#
#=((1+cos^2 theta)sin^2 theta)/sin^4 theta#
#=(1+cos^2 theta)/sin^2 theta#
#=1/sin^2 theta + cos^2 theta/sin^2 theta#
#=csc^2 theta +cot^2 theta#---> #cot^2 theta = csc^2 theta -1#
#=csc^2 theta+csc^2 theta -1#
#=2csc^2 theta -1#
#=#Right Side