Question 970944
tan^2x/secx+1=1-cosx/cosx
start with left side
{{{(tan^2(x))/(secx+1)
=(sin^2(x)/cos^2(x))/(1/cosx+1)
=(sin^2(x)/cos^2(x))/((1+cosx)/(cosx))
=(sin^2(x)/cos^2(x))*(cosx/(1+cosx))
=(1-cosx)(1+cosx)/(cosx*(1+cosx))=(1-cosx)/(cosx)}}}
verified: left side=right side