f(x)=10x² +100x +10
f(a)=10a² +100a +10 =b
f(b)=10b² +100b +10 =a => f(a+b)=10·(a+b)² +100·(a+b) +10 =10·(a² +2ab +b²) +100a +100b +10 =(10a² +100a) +(10b² +100b) +20ab +10=b-10 +a-10 +20ab +10=a+b +20ab -10 =f(a) +f(b) +20ab -10 => f(a+b)=f(a) +f(b) +20ab -10 sau f(a+b)=10·(a² +b² +10a +10b -2ab +1) .
