1.
[tex]dla \ \ x = 12,9 \ \ i \ \ y = 14,7\\\\\frac{x+y}{3} = \frac{12,9+14,7}{3} = \frac{27,6}{3} = \boxed{9,2}\\\\Odp. \ A.[/tex]
3.
[tex]dla \ \ x = -3 \ \ i \ \ y = 2\\\\a) \ (x+y)(x-y) =(-3+2)(-3-2) = -1\cdot(-5) = 5\\\\b) \ \frac{3xy+2}{2} =\frac{3\cdot(-3)\cdot2+2}{2}=\frac{2(3\cdot(-3)+1)}{2} = 3\cdot(-3)+1 =-9+1 = -8\\\\c) \ x(2x+y^{2}) = -3(2\cdot(-3)+2^{2}) = -3(-6+4) = -3\cdot(-2) = 6[/tex]
