Răspuns:
[tex]f:R->R, f(x)=2x-1[/tex]
a) Fie A(a,-a)
[tex]f(a)=-a => 2*a-1=-a <=>2a-1=-a=>3a-1=0=>3a=1=>a=\frac{1}{3} =>A(\frac{1}{3},-\frac{1}{3})[/tex]
b) [tex]S=f(1)+f(2)+.....+f(20)<=>(2*1-1)+(2*2-1)+...+(2*20-1)\\\\=1+3+5+...+39 <=> S=\frac{39*(39+1)}{2} =\frac{39*40}{2}=39*20= 780[/tex]
