如图,在Rt△ABC中,∠ACB=90°,CD⊥AB于D,设AC=b,BC=a,AB=c,CD=h. 求证:1/a2+1/b2=1/h2.

问题描述:

如图,在Rt△ABC中,∠ACB=90°,CD⊥AB于D,设AC=b,BC=a,AB=c,CD=h.
求证:

1
a2
+
1
b2
1
h2

证明:在直角△ABC中,∠ACB=90°,CD⊥AB,则△ACB∽△ADC∽△CDB,

CD
AC
=
BD
BC
,即
CD2
AC2
=
BD2
BC2

∵h2
1
a2
+
1
b2
)=
CD2
BC2
+
CD2
AC2
=
CD2
BC2
+
BD2
BC2

=
BC2
BC2
=1,
1
a2
+
1
b2
1
h2