# wrong answer from solve?

```
var('t')
test3 = -4*cos(t)^4 + 4*cos(t)^2 - 1
sage: solve(test3==0,t)
[]
```

When actually the equation is equivalent to (cos(t))^2 = 1/2 and it does have solutions.

wrong answer from solve?

```
var('t')
test3 = -4*cos(t)^4 + 4*cos(t)^2 - 1
sage: solve(test3==0,t)
[]
```

When actually the equation is equivalent to (cos(t))^2 = 1/2 and it does have solutions.

add a comment

1

```
sage: solve(test3==0,t,to_poly_solve=True)
[t == 1/4*pi + 1/2*pi*z35]
```

You do have to read the documentation of `solve?`

to see this option. It's not default because sometimes it will not return exact solutions.

So then, if solve returns [], that does not mean "there are no solutions". It means, "I didn't find any solutions". Similarly, if it does return a list of solutions, I guess that means "Here are the solutions I found", rather than, "Here are all the solutions." If this is the case, the documentation should say so up front. It says, "if there are no solutions it returns an empty list" but says nothing about the converse.

Asked: **
2016-01-22 10:03:04 -0500
**

Seen: **94 times**

Last updated: **Jan 22 '16**

Can someone help in finding code for solve function

Unable to make sense of Maxima expression

How to solve this equation with double square root?

obtain explicit solutions from "solve"

Get Sage to display the 2nd x value, when function is set to 0?

Trouble finding intersection of two functions

Cannot solve equation with two radical terms

How can I get back an expression for free variables in solve function.

Copyright Sage, 2010. Some rights reserved under creative commons license. Content on this site is licensed under a Creative Commons Attribution Share Alike 3.0 license.