kosine +(1/kosine) -1 = sekant +(1/sekant) -1
the 2 negativ 1's kansel, so yu hav
kosine+(1/lkosine)=sekant+(1/sekant)
But sekant=(1/kosine) so 2 terms kansel, so yer left with
kosine=(1/sekant)
But sekant=(1/kosine), so 1/sekant=kosine
so yu hav kosine=kosine
true