Question

как решить -(-у+2)^2+у(у+3) при у= 2\7

Answer 1

$-(-y+2)^2+y(y+3) = \\ = - (2 - y) ^{2} + {y}^{2} + 3y = \\ = - (4 - 4y + {y}^{2} ) + {y}^{2} + 3y = \\ = - 4 + 4y - {y}^{2} + {y}^{2} + 3y = \\ = 7y - 4 \\ \\ y = \frac{2}{7} \\ \\ 7 \times \frac{2}{7} - 4 = - 2$

Ответ: -2