( x + z ) while the other two sides are ( x + y ) and ( y + z ) for positive integers x , y , z .
In a certain right triangle, the hypotenuse equalsIf y + 4 = z and z > x , then compute x z .
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I was too close
I don't get it?
Is it possible split z 2 − 6 z − ( 2 x − 8 ) = 0 as z 2 − 6 z = 0 and 2 x − 8 = 0 so you obtain soon x = 4 and z = 6 ?
Since x+z is only 4 greater than x+y, we can find any right triangle that satisfies that one of the leg is 4 less than the hypotenuse. Note that y+z needs to have length between the other two, so the right triangle has small integer length. 6-8-10 comes up as a matching triangle. 8 is between the other two, which means y+z=8. y+z=8 =>y+y+4=8 =>y=2 =>x=4 =>z=6 Hence 6/4 = 1.5.
Or do it the stupid long algebra way. That's also correct.
Could you elaborate more on your explanation ? how many trials did you come up in order to reach your solution of 6-8-10 ? I want to measure the time spent doing this against the algebra path. It doesn't seem to be fast to reach the 6-8-10 triangle. Regards
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There are known, common, integer-sided right triangles. The most basic one, I think is a 3-4-5. (where 9 + 16 = 25). So integer multiples of 3-4-5 will also be right triangles ( I think). 6-8-10 is twice the sizes of a 3-4-5. So Glenn tried that one first because there is one leg that's the size of another + 4. And it worked.
Yeah hahaha :D
We have
y
+
4
=
z
, which is the same as
(
x
+
y
)
+
4
=
(
x
+
z
)
. Therefore, the hypotenuse is
4
more than one of the sides of the right angled triangle. Let
x
+
z
=
h
+
2
and
x
+
y
=
h
−
2
, for some
h
>
2
. Then by the Pythagoras' Theorem,
(
y
+
z
)
2
=
(
h
+
2
)
2
−
(
h
−
2
)
2
=
8
h
, so
8
h
must be a perfect square(and it is even). Let
8
h
=
4
k
2
, for some natural number
k
. Then
y
+
z
=
2
k
, and
x
+
y
=
2
k
2
−
2
so
k
is even and is greater than
2
. Finally,
z
>
x
implies
y
+
z
>
y
+
x
, or
2
k
>
2
k
2
−
2
, or
k
2
−
4
k
<
8
.
This means
(
k
−
2
)
2
<
1
2
.
Recall that
k
must be even, so
k
=
2
,
4
. But
k
>
2
. Therefore
k
=
4
. So the sides of the triangle are
2
×
4
=
8
,
2
4
2
−
2
=
6
,
and 10.
Note that
2
x
+
2
y
+
2
z
=
6
+
8
+
1
0
=
2
4
, so
x
+
y
+
z
=
1
2
Therefore
z
=
1
2
−
(
x
+
y
)
=
6
,
and
x
=
1
2
−
(
y
+
z
)
=
4
. So
x
z
=
1
.
5
Nice method
Your solution is elegant enough :)
y= 1 + 2 x − 1
and z= 1 + 2 x + 3
x,y,z all are positive integers and ,
from triangle inequality we can say z > x > y > 0 ,
z is also 4 more than 'y'
now,x=4 gives y=2 , z=6 therefore,
x z = 1 . 5
z=3 doesn't satisfy y+4=z but we have positive integers where they obey the above conditions
notice that i didn't work for the real triangle values for x,y,z
By Pythagoras, we have that
(x+z)^2 = (x+y)^2 + (y+z)^2
Substituting for y=z-4
(x+z)^2 = (x+z-4)^2 + (2z-4)^2
Expand, rearrange and factor yields
0 = (z-4)(z-2) - 2x
As x>0 ,(z-4)(z-2) must be >0 which implies that z<2 or z>4
Given that z>0, this implies that z=1 or z>4
As z>x, z=1 would imply that x (also a positive integer) would be 0, hence z cannot be = 1
Trialling z=5 (first integer greater than 4) yields a non-integer value for x
Trialling z=6 yields x=4 which satisfies all conditions and 6/4 = 1.5
x + y + y + z ≥ x + z
z ≥ 4
( x + y ) 2 + ( y + z ) 2 = ( y + z )
After much simplification
2 y 2 + 4 y − 4 x = 0
Discriminant = 4 2 − 4 ⋅ 2 ⋅ 4 x = 1 6 + 3 2 x
Discriminant needs to be a perfect square as x , y , z integers.
With some trial and error you get x = 4
And after that y = 2 and z = 6 and x = 4 .
So, x z = 4 6 = 1 . 5
By replacing y=z-4 and then using Pythagoras theorem We get z^2 - 6z +8 -2x=0 Now doing a bit of factorization we get (z-4) (z-2)=2*x
Now doing some logical comparison of both side we get z=6 ;x=4 So z÷x=1.5
What is that logical reasoning?
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By Pythagoras, we have that
( x + z ) 2 = ( x + y ) 2 + ( y + z ) 2
⟹ x 2 + 2 x z + z 2 = ( x 2 + 2 x y + y 2 ) + ( y 2 + 2 y z + z 2 )
⟹ 2 x z = 2 x y + 2 y z + 2 y 2 = 2 y ( x + y + z ) ⟹ x z = y ( x + y + z ) .
Given that y = z − 4 , this last equation then becomes
x z = ( z − 4 ) ( x + 2 z − 4 ) ⟹ x z = x z + 2 z 2 − 4 z − 4 x − 8 z + 1 6
⟹ z 2 − 6 z − ( 2 x − 8 ) = 0
⟹ z = 2 6 ± 3 6 + 4 ( 2 x − 8 ) = 3 ± 1 + 2 x .
Now since x and z must be positive integers, we will require that 1 + 2 x be a perfect square, and since 1 + 2 x is odd this perfect square must be that of an odd number. (Also, as this odd perfect square will be ≥ 3 we just need to look at the positive root, (since z > 0 ).) Thus for integers k > 0 we require that
1 + 2 x = ( 2 k + 1 ) 2 ⟹ 1 + 2 x = 4 k 2 + 4 k + 1 ⟹ x = 2 k ( k + 1 ) .
For k = 1 we have ( x , z ) = ( 4 , 6 ) , and for k = 2 we have ( x , z ) = ( 1 2 , 8 ) . In fact for k ≥ 2 we will have z < x , so since we must also satisfy the condition z > x we are left with the unique solution ( x , y , z ) = ( 4 , 2 , 6 ) , which yields a 6 / 8 / 1 0 right triangle and the ratio x z = 4 6 = 1 . 5 .