Question

先化简再求值。x-3分之3-x^-9分之18其中x=根号10-3

Answer 1

解：原式=3/(x-3)-18/(x+3)(x-3)
=(3x+9-18)/(x+3)(x-3)
=3(x-3)/(x+3)(x-3)
=3/(x+3)
∵x=√10-3
∴原式=3/√10=3/10*√10

Answer 2

因为x^2-9=(x+3)(x-3);
通分前一个分母并化简得：
[3(x+3)-18]/((x+3)(x-3))
=3(x-3)/((x+3)(x-3))
=3/(x+3)
=3/√10
=(3*√10)/10;