Description: Product of two negatives. Theorem I.12 of Apostol p. 18. (Contributed by NM, 30-Jul-2004) (Proof shortened by Andrew Salmon, 19-Nov-2011)
Ref | Expression | ||
---|---|---|---|
Assertion | mul2neg | |
Step | Hyp | Ref | Expression |
---|---|---|---|
1 | negcl | |
|
2 | mulneg12 | |
|
3 | 1 2 | sylan2 | |
4 | negneg | |
|
5 | 4 | adantl | |
6 | 5 | oveq2d | |
7 | 3 6 | eqtrd | |