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분수함수의 역함수는 마치 역행렬모양과 비슷한데

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그냥 실수k를 {(x y):x/y=k}로 생각하면 되는거였다
k ㅡ> Y=(ky, y)ㅡ>Z=AYㅡ>z=(ck+d)/(ak+b)
zㅡ>Y=A^-1Zㅡ>Z=(kz, z)ㅡ>k