Gọi $\overrightarrow{c}=m\overrightarrow{a+n\overrightarrow{b}, (m,n\in R)$
=> c→=(2m+n;−2m+4n)
Theo bài ra : c→=(5;0)
<=> {2m+n=5−2m+4n=0
<=> {m=2n=1
=> c→=2a→+b→
