Question

(9-y)^2-y(y+1) при y= -2/19

Answer 1

$(9-y)^2-y(y+1)=\\\\=9^2-2\cdot 9\cdot y+y^2-y\cdot y-y\cdot 1=\\\\=81\ \underline{\underline{-18y}}\ \underline{+y^2}\ \underline{-y^2}\ \underline{\underline{-y}}=81-19y$

$y=-\dfrac2{19}\\\\81-19\cdot\left(-\dfrac2{19}\right)=81+\dfrac{19\cdot 2}{19}=81+2=83$

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Использована формула квадрата разности:

$(a-b)^2=a^2-2ab+b^2$

Ответ: 83