Question

Se consideră f:R--->R
F(x)=2x+1. Să se calculeze:S=f(1)+f(2)+...+f(9)

Answer 1

f(1)+f(2)+f(3)+...+f(9)=
2*1+1+2*2+1+...2*9+1=
2*(1+2+3+...+9)+9=
2*45+9=
90+9=99

Answer 2

f(1)=3; f(2)=5; f(3)=7....f(9)=19. S=3+5+7+....+19; S=19+17+.....3 => 2S=22*9 => S=11*9=99