解:原公式= [x-√ (1+x？)]/{ [x+√(1+x？)] [x-√(1+x？)]}
= [x-√(1+x？)]/[x？-(1+x？)]
= [x-√(1+x？)]/(x？-1-x？)
=x-√(1+x？)
2.解:原公式= =7xy(8x？+2xy-3y)