第30題第30題第30題第30題

仲以為有三十題 =v=""
將a+1同a-1代入f(x)到
f(x)=x^2+x-1
f(a+1)=(a+1)^2+(a+1)-1=a^2+2a+1+a+1-1=a^2+3a+1
f(a-1)=(a-1)^2+(a-1)-1=a^2-2a+1+a-1-1=a^2-a-1
f(a+1)-f(a-1)=a^2+3a+1-(a^2-a-1)
=a^2-a^2+3a+a+1+1
=4a+2
=ans b

f(a+1)=(a+1)^2+(a+1)-1
=a^2+2a+1+a+1-1
=a^2+3a+1
f(a-1)=(a-1)^2+(a-1)-1
=a^2-2a+1+a-1-1
=a^2-a-1
So f(a+1)-f(a-1)=4a+2
So B

D.....(I am not very sure)

答:D!!!