X=1; y=-1/3 ______________________________________________________________________
-3x+7y+13x-7y-3 = -3*(-3)+7*(-15,01)+13*(-3)-7*(-15,01)-3*(-3) = 9-105,07-39+105,07+9 = 9-39+9 = -21
(a + b + c)(a + b + c)
= a(a + b + c) + b(a + b + c) + c(a + b + c)
= a2 + ab + ac + ba + b2 + bc + ca + cb + c2=a2 + b2 + c2 + 2ab + 2bc + 2ac