# Simplify doesn't work

**URL:** <https://community.wolfram.com/t/simplify-doesnt-work/7127>\
**Category:** Questions\
**Created:** [November 5, 2015, 6:23pm UTC](https://community.wolfram.com/t/simplify-doesnt-work/7127 "2015-11-05T18:23:47Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![knurtsj](https://avatars.discourse-cdn.com/v4/letter/k/ba8739/32.png) [@knurtsj](https://community.wolfram.com/u/knurtsj)\
**Post date:** [November 5, 2015, 6:23pm UTC](https://community.wolfram.com/t/simplify-doesnt-work/7127/1 "2015-11-05T18:23:47Z")

</div>

This snippet of code works in one program but the Simplify fails when I cut and pasted it into another program.

```
Jac := Simplify[JacArray];
JacTrans := Transpose[Jac];
Met := Simplify[JacTrans.Jac];

```

JacArray is a Jacobian matrix and Met is the corresponding Metric.  
The value of Met when it fails in my test case is `{cos[\[Theta]]^2 + sin[\[Theta]]^2, 0, 0, 0}, {0, r^2 (cos[\[Theta]]^2 + sin[\[Theta]]^2), 0, 0}`

It doesnt recognize that `cos[\[Theta]]^2 + sin[\[Theta]]^2` equals 1.  
FullSimplify doesnt help.

The main difference in the programs is that in the successful case I set Coordinates and query the system to get the Jacobian Matrix and in the unsuccessful case I put up a dialog that lets the user enter the Jacobian Matrix.

---

<div class="post-metadata">

**Author:** ![fkampas](https://yyz1.discourse-cdn.com/wolfram/user_avatar/community.wolfram.com/fkampas/32/41217_2.png) [@fkampas](https://community.wolfram.com/u/fkampas)\
**Post date:** [November 5, 2015, 7:13pm UTC](https://community.wolfram.com/t/simplify-doesnt-work/7127/2 "2015-11-05T19:13:58Z")

</div>

In[1]:= FullSimplify[Cos[[Theta]]^2 + Sin[[Theta]]^2]

```
Out[1]= 1

```

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<div class="post-metadata">

**Author:** ![knurtsj](https://avatars.discourse-cdn.com/v4/letter/k/ba8739/32.png) [@knurtsj](https://community.wolfram.com/u/knurtsj)\
**Post date:** [November 6, 2015, 12:03am UTC](https://community.wolfram.com/t/simplify-doesnt-work/7127/3 "2015-11-06T00:03:32Z")

</div>

I found the problem. In the program where I entered the Jacobian Matrix manually, I was typing `sin[\[Theta]]` instead of `Sin[\[Theta]]`.