证明:
(ac-bd)^2+(ad+bc)^2
=a^2c^2-2abcd+b^2d^2+a^2d^2+2abcd+b^2c^2
=a^2c^2+b^2d^2+a^2d^2+b^2c^2
=a^2*(c^2+d^2)+b^2*(c^2+d^2)
=(a^2+b^2)*(c^2+d^2)
=1*1
=1
证明:
(ac-bd)^2+(ad+bc)^2
=a^2c^2-2abcd+b^2d^2+a^2d^2+2abcd+b^2c^2
=a^2c^2+b^2d^2+a^2d^2+b^2c^2
=a^2*(c^2+d^2)+b^2*(c^2+d^2)
=(a^2+b^2)*(c^2+d^2)
=1*1
=1