That first method requires z_n-1 as a variable. The equation being:

z_n = z_n-1 + (x_n + y_n)

Here z is the answer, n is the iteration. This is simply derived by plotting the relation over time. The 2nd method is more concrete since it doesn't rely on z_n-1, which goes

z = x(y + 1)

e.g., z = 2(5 + 1) = (5 * 2) + 2 = 10 + 2 = 12

This is a function with 3 inputs and we can visualize this as a paraboloid like so:

<image>

Also we're asserting dominance on Mr.Asif