1＋sina／cosa＝(sin²a/2＋cos²a/2＋2sina/2cosa/2)／(cos²a/2－sin²a/2)
＝(sina/2＋cosa/2)²／[(cosa/2＋sina/2)(cosa/2－sina/2)]
＝(sina/2＋cosa/2)／(cosa/2－sina/2)
＝[√2(√2/2sina/2＋√2/2cosa/2)]／[√2(√2/2cosa/2－√2/2sina/2)]
＝(sina/2cosπ/4＋sinπ/4cosa/2)]／(cosπ/4cosa/2－sinπ/4sina/2)
＝sin(a/2＋π/4)／cos(π/4＋a/2)
＝tan(a/2＋π/4)
＝cot[π/2－(a/2＋π/4)]
＝cot(π/4－a/2)