(x-1)分之(x²+5x)-(x²-x)分之(7x²-x)
=(x-1)分之(x²+5x)-[x(x-1)]分之[x(7x-1)]
=(x-1)分之(x²+5x)-(x-1)分之(7x-1)
=(x-1)分之[(x²+5x)-(7x-1)]
=(x-1)分之(x²-2x+1)
=(x-1)分之(x-1)²
=x-1