1/a^2+1/b^2= a^2+b^2/a^2b^2=c^2/a^2b^2
根号（1\a^2+1\b^2)=c/ab=1/h
∴ab=ch得证
c^2\a^2b^2怎么就等于c\ab?
c^2\a^2b^2=(c\ab)^2
∴根号c^2\a^2b^2=c\ab