A linear combination of 1 - forms is also a 1 form.
Proof
Let
\[f, \: g\]
be real valued functions on a domain \[D \subseteq \mathbb{R}^n\]
and let \[\omega_1 ,\: \omega_2\]
be 1 - forms defined on \[D \]
&. Then\[\omega_{1 \mathbf{x}} =f_1 (\mathbf{x}) dx_1 +...+ f_n (\mathbf{x}) dx_n \]
\[\omega_{2 \mathbf{x}} =g_1 (\mathbf{x}) dx_1 +...+ g_n (\mathbf{x}) dx_n \]
\[\begin{equation} \begin{aligned} f \omega_{1 \mathbf{x}} +g \omega_{2 \mathbf{x}} &=f(f_1 (\mathbf{x}) dx_1 +...+ f_n (\mathbf{x}) dx_n )+ g(g_1 (\mathbf{x}) dx_1 +...+ g_n (\mathbf{x}) dx_n) \\ &=(ff_1 +gg_1)(\mathbf{x}) dx_1 +...+ (ff_n +gg_n)(\mathbf{x}) dx_n \end{aligned} \end{equation}\]
Which is of the same form as
\[\omega_1 ,\: \omega_2\]
.