Remove the Symbols of Grouping (I $21 a^{2}+2 b^{2}-$ $6\left(a b+3 a^{2}-5 b^{2}\right)$

Short Answer

Remove the symbols of grouping (i.e., brackets, braces, parentheses) and collect terms: $21 a^{2}+2 b^{2}-$ $6\left(a b+3 a^{2}-5 b^{2}\right)$