[tex]\sf a_{n} = a_{1}\cdot q^{(n - 1)} [/tex]
[tex]\sf a_{7} = a_{1}\cdot 2^{(7 - 1)} [/tex]
[tex]\sf 256= a_{1}\cdot 2^{6} [/tex]
[tex]\sf 256= a_{1}\cdot 64[/tex]
[tex]\sf 256= 64a_{1}[/tex]
[tex]\sf 64a_{1} = 256[/tex]
[tex]\sf a_{1} = \dfrac{256}{64} [/tex]
[tex]\red{\sf a_{1} = 4}[/tex]
