Let

M=[1039528710918]\displaystyle {M}={\left[\begin{array}{cccc} -{1}&{0}&{3}&-{9}\\{5}&-{2}&-{8}&-{7}\\-{10}&{9}&{1}&{8}\end{array}\right]}. Let A = MMT\displaystyle {M}\cdot{M}^{{T}}

(a) The dimension of A is ×\displaystyle \times , where CellA22=\displaystyle {A}_{{{22}}}=

(b) A is a matrix.