由面积相等得到:1/2ab=1/2ch,即ab=ch
平方得:a^2b^2=c^2h^2,即c^2/(a^2b^2)=1/h^2
c^2=a^2+b^2代入得(a^2+b^2)/a^2b^2=1/h^2
即1/a^2+1/b^2=1/h^2
A