a+b=√(√2008+√2007),
a-b=√(√2008-√2007)
(a+b)^2=a^2+2ab+b^2=√2008+√2007,
(a-b)^2=a^2-2ab+b^2=√2008-√2007,
相减,
4ab=2√2007,
ab=√2007/2