[질문] *일차함수f(x)=ax+2일때모든실수x에대하여f(x)=f-1(x)가성립하도록하는상수a값은?

y=ax+2역함수는x,y를바꾼x=ay+2,ay=x-2,y=(x-2)/a=f-1(x)죠.그럼ax+2=(x-2)/a,a^2x+2a-x+2=0,(a^2-1)x+2(a+1)=0입니다.모든실수x에대해성립하려면a=-1입니다.