a平方-4分之1- a-2分之1
=1/(a+2)(a-2)-1/(a-2)
=(1-a-2)/(a+2)(a-2)
=-(a+1)/(a+2)(a-2)
x平方-4x+4分之x平方-4 -x-2分之1
=(x+2)(x-2)/(x-2)²-1/(x-2)
=(x+2)/(x-2)-1/(x-2)
=(x+1)/(x-2)
x-1分之2+1-x分之x-1
=2/(x-1)+(x-1)/(1-x)
=(2-x+1)/(x-1)
=(3-x)/(x-1)