Rewrite the equations of the given boundary lines:
<em>y</em> = -<em>x</em> + 1 ==> <em>x</em> + <em>y</em> = 1
<em>y</em> = -<em>x</em> + 4 ==> <em>x</em> + <em>y</em> = 4
<em>y</em> = 2<em>x</em> + 2 ==> -2<em>x</em> + <em>y</em> = 2
<em>y</em> = 2<em>x</em> + 5 ==> -2<em>x</em> + <em>y</em> = 5
This tells us the parallelogram in the <em>x</em>-<em>y</em> plane corresponds to the rectangle in the <em>u</em>-<em>v</em> plane with 1 ≤ <em>u</em> ≤ 4 and 2 ≤ <em>v</em> ≤ 5.
Compute the Jacobian determinant for this change of coordinates:

Rewrite the integrand:

The integral is then

Answer:
The Length of <em>JK</em> is 10
Step-by-step explanation:
Because <<em>J </em>is congruent to <<em>L</em> we know that the triangle in question must be isosceles as in an isosceles triangle two angles opposite of each other are equal. (This is also true for equilateral triangles, however, in an equilateral triangle all sides must be congruent, so we can rule equilateral out as <em>LJ </em>is not congruent to <em>KL.) </em>This means that the triangle must be isosceles.
In an isosceles triangle the side opposite each other are congruent, and the angles opposite each other are congruent when split down the line of symmetry.
Therefor, the length of <em>JK </em>must be congruent to the length of <em>KL. </em>In other words if <em>JK </em>= 10, then <em>KL </em>must equal 10 as well.