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f : R ->R
f(3x+2)=x^2+3x-1
Calculati f(x).


Răspuns :

f(x) = ax² + bx +c
f(3x+2) = x² +3x - 1
f(3x+2) = (3x+2)²·a +b(3x+2) +c = (9x² +12x +4)·a + (3x+2)b +c =
= 9ax² +(12a +3b)x +4a+2b+c
9a = 1  a = 1/9 
12a+3b = 3    4a+b = 1    4/9 +b = 1  b = 5/9
4a+2b+c = - 1    4/9 +10/9 +c = - 1  c = - 23/9
f(x) = 1/9 ·x² + 5/9 ·x - 23/9