This is because of the order that Lua does mathematical operations - it’s called precedence and you can read a bit about it here.

If you have a look at that page you can see that the exponential operation is executed before unary negation - that means your second operation (and anywhere else you stick a negative sign) is roughly equivalent to:

-0.05 * -1 * 1 ^ 2

And from PEDMAS you can see that the square term will be resolved first, and then the rest multiplied together to get a positive number.

The other operations give a negative as using a variable evaluates the unary operation first, making the equation equivalent to: