根号下大于等于0
6-5x-x^2>=0
x^2+5x-6<=0
(x+6)(x-1)<=0
-6<=x<=1
真数大于0
x+3>0
x>-3
分母不等于0
lg(x+3)≠0=lg1
所以x+3≠1
x≠-2
综上,定义域
(-3,-2)∪(-2,1]