      
1.       :−
 +  + =0
(
,   ;   ≠ 0
)
2. ℎ     ℎ .
3. ℎ         :−
  /   / →
≠
  /   /  →
=
≠
 /   /  →
=
=
4. ℎ         :−
ℎ ℎ
 ℎ
 ℎ
  ℎ