Question

f(1)+f(2)+......+f(49)=
f(x)= x-3

Answer 1

Răspuns:

f(1)=1-3=-2 ;   f(2)=2-3=-1 ;   f(3)=3-3=0 ; ... f(49)=49-3=46 ;   1+2+...+46=(1+46)*46/2=47*23=1081 ;   1081-3=1078

Explicație pas cu pas:

Answer 2

$\it f(x)=x-3\\ \\ f(1)+f(2)+f(3)+\ ...\ +f(49)=(1-3)+(2-3)+(3-3)+(4-3)+(5-3)+\\ \\ +(6-3)+(7-3)+\ ...\ +(49-3)=-2-1+0+1+2+3+4+\ ...\ +46=\\ \\= -3+\dfrac{46\cdot47}{2}=-3+23\cdot47=-3+1081=1078$