SOLUTION: a rectangle has length a, width b and diagonal c. All three are integers less than 100, c is 40 units less than the sum of a and b, and they have no common factors. find a, b, c

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Question 262758: a rectangle has length a, width b and diagonal c. All three are integers less than 100, c is 40 units less than the sum of a and b, and they have no common factors. find a, b, c
Answer by drk(1908) About Me  (Show Source):
You can put this solution on YOUR website!
FRom the given, we know that
a%5E2+%2Bb%5E2+=+c%5E2
we also now that c= a+b - 40
By substitution, we get
a%5E2+%2B+b%5E2+=+%28a%2Bb-40%29%5E2
expanding the right side, we get
a%5E2+%2B+b%5E2+=+a%5E2+%2B+b%5E2+%2B+1600+%2B2ab+-80a+-+80b
subtracting a^2 and b^2 from both sides, we get
0+=+1600+%2B+2ab+-+80a+-+80b
or
80a+%2B+80b+-+2ab+=+1600
we can solve for a in terms of b. factor out 2a to get
2a%2840+-b%29+%2B+80b+=+1600
subtract 80b to get
%282a%29%2840-b%29+=+1600+-+80b
divide by 2(40-b) to get
a+=+%2880%2820-b%29%29%2F%282%2840-b%29%29
which simplifies to
a+=+%2840%2A%2820-b%29%29+%2F+%2840-b%29
At this point we know that b <= 20 OR b > 40.
Since we want integers for a and b, here are a few options in (a,b) form:
(8,15) or (15,8)
If we use
(8,15), then c = 17 and all 3 share no common factors. But this doesn't satisfy our restrictions.
Our only new options for (a,b,c) are:
(67, 72, 97)