I was reading this Lang's book where he says
F3: For every injection $0\rightarrow E'\rightarrow E$, we have $0\rightarrow E'\otimes F\rightarrow E\otimes F$
F1: For every exact sequence $E'\rightarrow E\rightarrow E''$, we have an exact sequence $E'\otimes F\rightarrow E\otimes F\rightarrow E''\otimes F$.
How do I show from F3 to F1? Lang says consider the kernel and image of the mapping $E'\rightarrow E$, but I couldn't figure out why. Thanks!