Answer
$\dfrac{4}{3}$
Work Step by Step
The point of intersection gives results: $\sqrt {1-x^2}=0 \implies 1-x^2=0 \\ \implies x =\pm 1$
Therefore, the volume of a solid can be computed as:
$V=\int_a^b A(x) dx=\int_{-1}^1 4(1-x^2)^2 \ dx \\=2 \int_0^1 (1-x^2) \ dx \\= 2[x-\dfrac{1}{3}x^3]0^1 \\=2 (1-\dfrac{1}{3}) \\=\dfrac{4}{3}$
