x = cy + bz
y = az + cx
y = az + c2y + cb
(1 - c2)y = (a+bc)z
meanwhile
z = bx + ay
z = bcy + b2z + ay
(1 - b2)z = (a + bc)y
from first set:
y/(a+bc) = z/(1 - c2)
(a + bc)y/(1 - b2) = z
multiply left equation to left.. and right equation to right equation also .
y2/(1 - b2) = z2/(1 - c2)
then you can continue with the rest of the equation