8. Sabendo que $x=2-[5+(-3+6)-(+7)] e y=3-[8-(-2-4)-9]$, calcule o valor de $2 x^{2}-3 y$.
\(\boxed{8}\)
Step 1 :\(x = 2 - [5 + (-3 + 6) - (+7)]\)
Step 2 :\(x = 2 - [5 + 3 - 7]\)
Step 3 :\(x = 2 - [1]\)
Step 4 :\(x = 1\)
Step 5 :\(y = 3 - [8 - (-2 - 4) - 9]\)
Step 6 :\(y = 3 - [8 - (-6) - 9]\)
Step 7 :\(y = 3 - [-6]\)
Step 8 :\(y = -2\)
Step 9 :\(2 x^{2} - 3 y = 2 (1)^{2} - 3 (-2)\)
Step 10 :\(2 x^{2} - 3 y = 2 + 6\)
Step 11 :\(2 x^{2} - 3 y = 8\)
Step 12 :\(\boxed{8}\)