Difference between Matlab and Wolfram Alpha

These problems might occure frequently due to the varied syntax. This time it's about:

solve(x^2-8*x+15<=1)

what gives (according to Matlab): pi and 4. That's wrong or not what I ask for. In contrast Wolfram Alpha gives after typing in the same piece of code the correct solution (in my point of view.) Why is that?

Answer 1

[Jesús Zambrano]

Hi Niklas,

You need to set 'ReturnConditions' to true to return any parameters in the solution and conditions on the solution. Therefore,

S = solve(x^2-(8*x)+15<=1, 'ReturnConditions',true);
S.conditions,

ans =
 x <= 2^(1/2) + 4 & 4 - 2^(1/2) <= x
                       in(y, 'real')

which is the solution interval: 2.5858 <= x <= 5.4142

Answer 2

[Cam Salzberger]

Hey Niklas,

Technically, both pi and 4 are "correct" results, as if you plug them in, they will fulfill the condition. I think what you are looking for is using the solution = solve(___, "ReturnConditions", true) syntax, as suggested by the solving inequalities example in the documentation.

Also, it would generally be helpful to post what you got from Wolfram as well, so we know what you're expecting.

-Cam

[Niklas Kurz]

Thank you, guys

x <= 2^(1/2) + 4 & 4 - 2^(1/2) <= x

is what I'm looking for.