giobas
The three sides of triangle have length p, q and r, each an integer. Is this triangle right triangle?
(1) The perimeter of the triangle is an odd integer.
(2) If the triangle's area is doubled, the result is not an integer.
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Responding to a pm:
A few things about primitive pythagorean triplets (not multiples of other pythagorean triplets) a, b, c where c is the hypotenuse.
1. One of a and b is odd and the other is even.
2. c is odd.
(3, 4, 5), (5, 12, 13), (8, 15, 17) etc
The non-primitive triplets are made by multiplying each member of the primitive triplet by an integer n greater than 1. Depending on whether n is odd or even, the three sides will be (Odd, Even, Odd) or (Even, Even, Even).
Given:
p, q and r are all integers.
(1) The perimeter of the triangle is an odd integer.
The perimeter of a right triangle can never be odd.
Odd + Even + Odd = Even
Even + Even + Even = Even
Hence, the perimeter will be even in all cases.
(2) If the triangle's area is doubled, the result is not an integer.
If p, q and r are the sides of a right triangle such that r is the hypotenuse (could be any of p, q, r),
Area of this triangle = (1/2)*p*q
Double of area of this triangle = p*q
This has to be an integer.
But we know that this is not an integer. In that case, this triangle cannot be a right triangle.
If it is not a right triangle, double the area will be base*altitude. The altitude would not be an integer in this case.
Answer (D)