computing time It takes an hour to burn a rope. Now there are n ropes of the same material thickness. How can we determine an hour and 15 minutes by burning a rope?

Premise: need three
Rope a burns from both ends and rope B burns from one end at the same time. When rope a burns out, destroy rope B and rope C burns from both ends at the same time. When rope C burns out, rope B burns from both ends and ends in 1 hour and 15 minutes

cycle
1 321321 × 123 minus 123123 × 321 2 369 × 135135 minus 369369369 × 1353 1995 × 1995 minus 1994 × 1994

321321×123-123123×321 =321*1001*123-123*1001*321=0369×135135135-369369369×135 =369*135*1001001-369*1001001*135=01995×1995-1994×1994 =1995*(1994+1)-1994*(1995-1)=1995*1994+1995-1994*195+19...

A mathematical problem of period
How to find the minimum positive period of F (x) = sin2x-cos2x?
Is it Pai?

F (x) = sin2x-cos2x = √ 2Sin (2x - π / 4) the period is π

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computing time It takes an hour to burn a rope. Now there are n ropes of the same material thickness. How can we determine an hour and 15 minutes by burning a rope?