1. A={x| x<<3 } , B={x|xB is subset of A=> a≤3A是B的真子集=> a<让瞎32.a> b => a^2> b^2 (错)e.g.a= 1, b =-31>-3但 1 <返锋 93.x^2+bx+b>0△ = b^2-4b >0 => b(b-4)>0 b< 0 or b>4 #4. 题目不清漏滑晌楚5. f(0) =1, ( I suppose) f(x+1)-f(x)=2xput x=0f(1)-f(0)= 0 f(1) = 1put x=2f(2)-f(1) = 2 f(2) = 3 let f(x) = ax^2+bx+c f(0) = c =1f(x) = ax^2+bx +1f(1) = a + b +1 = 1 b = -af(2) = 4a+2b+1 = 3 2a = 2 a = 1 b=-1f(x) = x^2-x+1
a<3a<=3