I have the following representation:

$(a+{\beta}^{\prime}X{)}^{2}$

where a is a constant and both $\beta $ and X are k by 1 vectors.

The representation is further written as follows:

${a}^{2}+2a{\beta}^{\prime}X+{X}^{\prime}\beta {\beta}^{\prime}X)$

While the first part is clear to me, I struggle to understand why it is shown once with ′ (X′ and ${\beta}^{\prime}$) and once without ′ (X and $\beta $).

$(a+{\beta}^{\prime}X{)}^{2}$

where a is a constant and both $\beta $ and X are k by 1 vectors.

The representation is further written as follows:

${a}^{2}+2a{\beta}^{\prime}X+{X}^{\prime}\beta {\beta}^{\prime}X)$

While the first part is clear to me, I struggle to understand why it is shown once with ′ (X′ and ${\beta}^{\prime}$) and once without ′ (X and $\beta $).