x_{max }= 3 \\ y_{max } = y(x_{max }) = \\ = y(3) = - {3}^{2} + 6 \cdot 3 + 3 = \\ = - 9 + 18 + 3 = 12" alt=" y(x) = - {x}^{2} + 6x + 3 \\ y'(x) = - 2x + 6 = 0 \\ = > x_{max }= 3 \\ y_{max } = y(x_{max }) = \\ = y(3) = - {3}^{2} + 6 \cdot 3 + 3 = \\ = - 9 + 18 + 3 = 12" align="absmiddle" class="latex-formula">