((90*(60/360))-(60-10*5))/(1-(5/60))
=((90/6)-(60-50))/(1-1/12)
=(15-10)/(11/12)
=5/(11/12)
=5*(12/11)
=60/11
=5又(5/11)分
(5*10-(90*(60/360))/(1-5/60)
=(50-15)/(1-1/12)
=35/(11/12)
=35*(12/11)
=420/11
=38又(2/11)分
在10点与11点之间的10点5又(5/11)分时,时针与分针首次垂直,10点38又(2/11)分时,时针与分针第二次垂直.