令y=1
f(x+1)=f(x)+x
构造一个数列使得
a(x+1)=f(x+1)
ax=f(x)
所以 a(x+1)=ax+x
所以a(x+1)=ax+x=a(x-1)+(x-1)+x
=.
=a1+1+2+.+x
ax=a1+1+2+...+(x-1)
=1+(x-1)x/2
所以f(x)=(x-1)x/2 +1
令y=1
f(x+1)=f(x)+x
构造一个数列使得
a(x+1)=f(x+1)
ax=f(x)
所以 a(x+1)=ax+x
所以a(x+1)=ax+x=a(x-1)+(x-1)+x
=.
=a1+1+2+.+x
ax=a1+1+2+...+(x-1)
=1+(x-1)x/2
所以f(x)=(x-1)x/2 +1