平面向量$\stackrel{\rightharpoonup }{a}=(1,2),\stackrel{\rightharpoonup }{b}=(4,2),\stackrel{\rightharpoonup }{c}=m\stackrel{\rightharpoonup }{a}+\stackrel{\rightharpoonup }{b}(m\in R)$，且$\stackrel{\rightharpoonup }{c}$与$\stackrel{\rightharpoonup }{a}$的夹角等于$\stackrel{\rightharpoonup }{c}$与$\stackrel{\rightharpoonup }{b}$的夹角，则$m=$.