[tex]a\cdot b = 79 \\ b\cdot c = 49\\ -----($scadem)$ \\ \\ a\cdot b-b\cdot c = 79-49 \\ \\ b\cdot (a-c) = 30[/tex]
Altfel scris:
[tex]a\cdot b = 79 \\ b\cdot c = 49 \\ \\ \Rightarrow b\cdot (a-c) = b\cdot a-b\cdot c = {a\cdot b}-b\cdot c = 79-49 = 30[/tex]
