Даны векторы \(\displaystyle \overrightarrow {a} (2;3),\) \(\displaystyle \overrightarrow {b}(-3;7),\) \(\displaystyle \overrightarrow {c} (7;-1).\)

Найдите скалярное произведение векторов \(\displaystyle \overrightarrow {a}+\overrightarrow {b}\) и \(\displaystyle \overrightarrow {c} .\)

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