The two hands of a clock are so situated that, reckoning as minute points past XII, one is exactly the square of the distance of the other.
Determine all possible times that conform to the given conditions.
**** Adapted from an original problem by H. E. Dudeney.
We're measuring angle clockwise from the top so that one revolution equals 60 units, so if the position of the minute hand is to be the square of the position of the hour hand, it cannot be as much as 2 PM, as even at 2 PM, the square of 10 is 100 -- outside the range of a clocface. In every hour a time can be reached where the minute hand position squared equals the hour hand position.
syms m
for h=0:11
hh=5*h+m/60;
mh=m;
% 1st: hh^2 = mh
% m=(5*h+m/60)^2 = 25*h^2 + m^2/3600 + h*m/6
% m^2/3600 + h*m/6 - m + 25*h^2 = 0
disp(h)
s=roots([1/3600,h/6-1,25*h^2]);
disp([s,5*h+s/60])
%then min hand is sqrt of hour hand
s=roots([1 -1/60 -5*h]);
disp([s,5*h+s/60])
disp('--------')
end
solves the quadratic equations, including spurious results, so we have to throw out 3 out of 4 equation solutions:
>> whatIsTheTime
0
0 0
3600 60
0 0
0.0166666666666667 0.000277777777777778
--------
1
2969.69384566991 54.4948974278318
30.3061543300931 5.50510257216822
2.24441683902905 5.03740694731715
-2.22775017236238 4.96287083046063
--------
2
2239.23048454133 47.3205080756888
160.769515458674 12.6794919243112
3.17062197361341 10.0528436995602
-3.15395530694675 9.94743407821755
--------
3
900 30
900 30
3.8813256447696 15.0646887607462
-3.86465897810293 14.9355890170316
--------
4
Column 1
600 + 1039.23048454133i
600 - 1039.23048454133i
Column 2
30 + 17.3205080756888i
30 - 17.3205080756888i
4.4804770524511 20.0746746175409
-4.46381038578443 19.9256031602369
--------
5
Column 1
300 + 1469.69384566991i
300 - 1469.69384566991i
Column 2
30 + 24.4948974278318i
30 - 24.4948974278318i
5.00834027777296 25.0834723379629
-4.99167361110629 24.9168054398149
--------
6
Column 1
0 + 1800i
0 - 1800i
Column 2
30 + 30i
30 - 30i
5.48556524776278 30.0914260874627
-5.46889858109611 29.9088516903151
--------
7
Column 1
-300 + 2078.46096908265i
-300 - 2078.46096908265i
Column 2
30 + 34.6410161513775i
30 - 34.6410161513775i
5.92441898555681 35.0987403164259
-5.90775231889014 34.9015374613518
--------
8
Column 1
-600 + 2323.79000772445i
-600 - 2323.79000772445i
Column 2
30 + 38.7298334620742i
30 - 38.7298334620742i
6.33289414373309 40.1055482357289
-6.31622747706642 39.8947295420489
--------
9
Column 1
-900 + 2545.58441227157i
-900 - 2545.58441227157i
Column 2
30 + 42.4264068711929i
30 - 42.4264068711929i
6.71654244191399 45.1119423740319
-6.69987577524732 44.8883354037459
--------
10
Column 1
-1200 + 2749.5454169735i
-1200 - 2749.5454169735i
Column 2
30 + 45.8257569495584i
30 - 45.8257569495584i
7.07940605566086 50.1179901009277
-7.06273938899419 49.8822876768501
--------
11
Column 1
-1500 + 2939.38769133981i
-1500 - 2939.38769133981i
Column 2
30 + 48.9897948556636i
30 - 48.9897948556636i
7.42453650237101 55.1237422750395
-7.40786983570434 54.8765355027383
--------
At 12:00 exactly, both hands are at 0, and 0^2 = 0.
At 1:02.24441683902905 the minute hand is at the minute portion shown, and the hour hand is at 5.03740694731715, the square of the minute hand position.
At 1:30.3061543300931 the hour hand is at the square root of that minute hand position: 5.50510257216822. That's the last time that the minute hand will the at the square of the hour hand.
At 2:03.17062197361341 the hour hand will be at 10.0528436995602.
At 3:03.8813256447696 the hour hand will be at 15.0646887607462.
At 4:04.4804770524511 the hour hand will be at 20.0746746175409.
At 5:05.00834027777296 the hour hand will be at 25.0834723379629.
At 6:05.48556524776278 the hour hand will be at 30.0914260874627.
At 7:05.92441898555681 the hour hand will be at 35.0987403164259.
At 8:06.33289414373309 the hour hand will be at 40.1055482357289.
At 9:06.71654244191399 the hour hand will be at 45.1119423740319.
At 10:07.07940605566086 the hour hand will be at 50.1179901009277.
At 11:07.42453650237101 the hour hand will be at 55.1237422750395.
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Posted by Charlie
on 2023-09-12 09:07:15 |