把值代入不就算出来了?f(负根号2)=3*2+5倍根号2+2=5+5倍根号2
f(-a)=3a^2+5a+2
f(a+3)=3(a+3)^2-5(a+3)+2=3a^2+13a-4
f(a)+f(3)=3a^2-5a+2+27-15+2=3a^2-5a+16