To prove #cos x / (sec x - tan x) = (1 + sin x)#
L H S # = cos x / ((1/cos x) - (sin x / cos x)# as #color(blue)(sec x = 1/cos x, tan x = sin x / cos x#
#=> cos x / ((1 - sin x) / cos x)# as #color(green)(cos x # is the L C M of Denominator.
#=> cos^2 x / (1 - sin x)#
#=> = (1 - sin^2 x) / (1 - sin x)# as #color(blue)(cos^2x = 1 - sin^2x#
#=> ((1+ sin x) *color(red)(cancel (1 - sin x))) /color(red)(cancel (1 - sin x))#
#=> 1 + sin x#
Q E D