(x—1)分之1—(x平方—1)分之2=(x+1)/(x²-1) - 2/(x²-1)=(x-1)/(x²-1)=1/(x+1)(a—1)分之(a+1)—(a+1)分之(a—1)=(a+1)²/[(a+1)(a-1)] - (a-1)²/[(a+1)(a-1)]=[(a+1)² - (a-1)²]...