How to calculate (1 + 2 / 1 + 3 / 1 + 4 / 1) * (2 / 1 + 3 / 1 + 4 / 1) - (1 + 2 / 1 + 3 / 1 + 4 / 1 + 5 / 1) * (2 / 1 + 3 / 1 + 4 / 1)

How to calculate (1 + 2 / 1 + 3 / 1 + 4 / 1) * (2 / 1 + 3 / 1 + 4 / 1) - (1 + 2 / 1 + 3 / 1 + 4 / 1 + 5 / 1) * (2 / 1 + 3 / 1 + 4 / 1)

The second bracket is 2 / 1 + 3 / 1 + 4 / 1 + 5 / 1
Let a = 2 / 1 + 3 / 1 + 4 / 1
Then the original formula = (1 + a) (a + 5 / 1) - (1 + A + 5 / 1) a
=(1+a)a+5/1(1+a)-(1+a)a-5/1a
=5/1(1+a)-5/1a'
=5/1+5/1a-5/1a
=5/1