Question

设x、y∈R,且y=根号下1-x2+根号下x2-1除以x+1,求lg（x+y）的值

Answer 1

根号必须是大于等于零,则1-x^2>=0且x^2-1>=0

得x^2=1,又分母x+1不=0,那么可得x=1

y=0+0/(1+1)=0

lg(x+y)=lg1=0