It is known that a / b = B / C = C / A, and A-B + C is not equal to zero. It is proved that a + B + C is not equal to zero

It is known that a / b = B / C = C / A, and A-B + C is not equal to zero. It is proved that a + B + C is not equal to zero

In fact, if a / b = B / C = C / a = k, then a / b * B / C * C / a = 1 = K & sup3;, so k = 1, that is, a = b = C
And A-B + C = a ≠ 0
So a + B + C = 3A ≠ 0

Prove that a ^ 2-B ^ 2-2ab is equal to zero

This formula is not equal to zero
For example: a = 0, B = 1
The value of this algebra is - 1
Is there an error in the input?

(1) If a / b = C / D (BD ≠ 0), then a / (a-b) = A / (C-D). Please explain the reason

（1）∵ （x+y):y=4:5
∴5x+5y=4y
∴y=-5x
∴x/y=-1/5
Is the second question wrong