1 | initial version |

WorksForMe(TM):

```
sage: var("t")
t
sage: theta=function("theta")
sage: A=cos(theta(t))
sage: diff(A,t)
-sin(theta(t))*diff(theta(t), t)
sage: var("B,C")
(B, C)
sage: diff(A,t).subs([diff(theta(t),t)==B,theta(t)==C])
-B*sin(C)
```

But remember that in the `subs`

method, the single equal sign (which is

2 | No.2 Revision |

WorksForMe(TM):

```
sage: var("t")
t
sage: theta=function("theta")
sage: A=cos(theta(t))
sage: diff(A,t)
-sin(theta(t))*diff(theta(t), t)
sage: var("B,C")
(B, C)
sage: diff(A,t).subs([diff(theta(t),t)==B,theta(t)==C])
-B*sin(C)
```

But remember that in the `subs`

method, the single equal sign (which is a marker for keywords in a function call) is accepted for a *single* substitition. To to multiple substitutions, use either a list of equations (whose sides are separated by `==`

, i. e. a *double* equal sign) or a dictionary.

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