(a^2+b^2)(c^2+d^2)
=a^2c^2+a^2d^2+b^2c^2+b^2d^2=40,
∴a^2d^2+b^2c^2=40-(a^2c^2+b^2d^2)
(ad-bc)^2
=a^2d^2-2abcd+2b^2c^2
=40-(a^2c^a+2abcd+b^2c^2)
=40-(ac+bd)^2
=40-4
=36.
(a^2+b^2)(c^2+d^2)
=a^2c^2+a^2d^2+b^2c^2+b^2d^2=40,
∴a^2d^2+b^2c^2=40-(a^2c^2+b^2d^2)
(ad-bc)^2
=a^2d^2-2abcd+2b^2c^2
=40-(a^2c^a+2abcd+b^2c^2)
=40-(ac+bd)^2
=40-4
=36.