f(a)-f(a+1)=-13
(a²+2a²+3)-[(a+1)²+2a(a+1)+3]=-13
3a²+3-[a²+2a+1+2a²+2a+3]=-13
3a²+3-[3a²+4a+4]=-13
3a²+3-3a²-4a-4=-13
-4a-1=-13
a=3
所以:实数a的值是a=3
f(a)-f(a+1)=-13
(a²+2a²+3)-[(a+1)²+2a(a+1)+3]=-13
3a²+3-[a²+2a+1+2a²+2a+3]=-13
3a²+3-[3a²+4a+4]=-13
3a²+3-3a²-4a-4=-13
-4a-1=-13
a=3
所以:实数a的值是a=3