Metamath Proof Explorer


Theorem divmuldivi

Description: Multiplication of two ratios. Theorem I.14 of Apostol p. 18. (Contributed by NM, 16-Feb-1995)

Ref Expression
Hypotheses divclz.1
|- A e. CC
divclz.2
|- B e. CC
divmulz.3
|- C e. CC
divmuldiv.4
|- D e. CC
divmuldiv.5
|- B =/= 0
divmuldiv.6
|- D =/= 0
Assertion divmuldivi
|- ( ( A / B ) x. ( C / D ) ) = ( ( A x. C ) / ( B x. D ) )

Proof

Step Hyp Ref Expression
1 divclz.1
 |-  A e. CC
2 divclz.2
 |-  B e. CC
3 divmulz.3
 |-  C e. CC
4 divmuldiv.4
 |-  D e. CC
5 divmuldiv.5
 |-  B =/= 0
6 divmuldiv.6
 |-  D =/= 0
7 2 5 pm3.2i
 |-  ( B e. CC /\ B =/= 0 )
8 4 6 pm3.2i
 |-  ( D e. CC /\ D =/= 0 )
9 divmuldiv
 |-  ( ( ( A e. CC /\ C e. CC ) /\ ( ( B e. CC /\ B =/= 0 ) /\ ( D e. CC /\ D =/= 0 ) ) ) -> ( ( A / B ) x. ( C / D ) ) = ( ( A x. C ) / ( B x. D ) ) )
10 1 3 7 8 9 mp4an
 |-  ( ( A / B ) x. ( C / D ) ) = ( ( A x. C ) / ( B x. D ) )