Răspuns:
Explicație pas cu pas:
Cumva asa?
f(5)=15
15= 5a+b=> b= 15-5a
f(1)+ f(2)+f(3)= 6a+b
f(1)= a+b
f(2)=2a+b
f(3)=3a+b
a+b+ 2a+b+ 3a+b= 6a+b
6a+ 3b= 6a+b
6a-6a+3b= b
3b=b=> 3b-b=0=> 2b=0=> b=0
b=15-5a
0=15-5a
-15=-5a
(-15) :(-5)= a
a=3
Verificam
a=3 si b=0
f(1)= 3 ori 1+ 0= 3
f(2)= 3 ori 2+0= 6
f(3)= 3 ori 3 +0=9
f(1)+f(2)+ f(3)= 6a+b?
3+ 6+9= 6 ori 3 +0?
18= 18 (adevarat)
F(5)=15?
f(5)= 3 ori 5+ 0= 15 (adevarat)
