Simplify (a^2+b^2)(c^2+d^2)

$(a^{2} + b^{2}) (c^{2} + d^{2})$

Apply the distributive property.

$a^{2} (c^{2} + d^{2}) + b^{2} (c^{2} + d^{2})$

Apply the distributive property.

$a^{2} c^{2} + a^{2} d^{2} + b^{2} (c^{2} + d^{2})$

Apply the distributive property.

$a^{2} c^{2} + a^{2} d^{2} + b^{2} c^{2} + b^{2} d^{2}$