Question 956525
The description tells very little about your triangle.  You need more information or the description is lacking and no solution of x.


BUT you could test the three given expressions to see if they conform to Pythagorean Theorem.   You may need to setup three equations to find out.


Are ANY one of these true?
-
{{{(x+20)^2+(2x-20)^2=(2x-40)^2}}}
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{{{(2x-20)^2+(2x-40)^2=(x+20)^2}}}
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{{{(x+20)^2+(2x-40)^2=(2x-20)^2}}}


If ONE of those is true, then the expressions for the sides are of a right triangle.  You still cannot solve for x, but you could find the angle measures.


I have not worked through this any further, so how far you can go with this is uncertain.


AFTER-THOUGHT.
Triangle Inequality Theorem could give possible set of values for x.  You would work from three inequality statements according to this theorem.


FROM PERSONAL COMMENT:
If the triangle is scalene, all you can do is use triangle-inequality theorem to solve for possible set of values for x.   The problem description and question give nothing more to work with.  What formula do you expect to use?