在公式1R=1r1+1r2中,(r1+r2≠0),用r1、r2表示R是( ) A.R=r1+r2 B.R=r1r2 C.1R=r1+r2r1r2 D.R=r1r2r1+r2
问题描述:
在公式
=1 R
+1 r1
中,(r1+r2≠0),用r1、r2表示R是( )1 r2
A. R=r1+r2
B. R=r1r2
C.
=1 R
r1+r2
r1r2
D. R=
r1r2
r1+r2
答
两边同乘以最简公分母Rr1r2,得
r1r2=(r1+r2)R
两边同除以r1+r2,得R=
.故选D.
r1r2
r1+r2