Jacobian Change of Variables Question

Homework Statement

Evaulate the integral making an appropriate change of variables.

$$\int\int_R(x+y)e^{x^2-y^2}dA$$ where R is the parallelogram enclosed by the lines x-2y=0, x-2y=4, 3x-y=1, 3x-y=8 .

The Attempt at a Solution

I'm not sure what change of variables I should make. The way the region R is defined suggests that I should make the substitution u=x-2y, v=3x-y. Which maps the region r into a square s which is a simple region to integrate over. However, solving for x and y you obtain x=(1/5)(2v-u), y= (1/5)(v-3u). Changing the integral using these substitutions yields

$$\frac{1}{5}(3v-4u)e^{\frac{1}{25}(-8u^2+2uv+3v^2)}$$ which is not integrable.

Likewise, if you select a substitution which makes the integrand simple, say u=x+y and v=x-y you obtain a parallelogram as the region s which is not simple to integrate over. Am I missing something?

Homework Helper
Making the integrand simple is usually more important than making the borders simple. I would go with the parallelogram.

spamiam
How can you rewrite the exponent?

$$\int_{0.2}^{1.6}\int_{-2u+1}^{3u}ve^{uv}dvdu+\int_{1.6}^{1.8}\int_{-2u+1}^{-2u+8}ve^{uv}dvdu+\int_{1.8}^{3.2}\int_{3u-8}^{-2u+8}ve^{uv}dvdu$$