The marginal density of $X$ is given by
$$
f_X(x) = \int_{-\infty}^{\infty} f(x, y) dy = \int_{0}^{\infty} xy dy = \frac{1}{2}x,
$$
for $0 < x < 1$ and $0$ otherwise. Similarly, the marginal density of $Y$ is given by
$$
f_Y(y) = \int_{-\infty}^{\infty} f(x, y) dx
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