解 (a+2)c=a+2
ac+2c=a+2
ac-a=2-2c
a(c-1)=2-2c
a=(2-2c)/(c-1) = 2(1-c)/(c-1) = -2(c-1)/(c-1) =-2
a的平方+2a+1=(a+1)(a+1)=(-2+1)(-2+1)=1