I'm not sure which numbers you are referring to, but 3 has the same absolute value as -3, and 7 has the same absolute value as -7, just for an example.
When there's more than one letter, and you just have to solve for one variable, you can just solve it like you would any other equation. Treat the other variables like numbers and add, subtract, multiply, and divide them to both sides of the equation in order to isolate the variable you want to solve for.
Answer:
it`s acute because the angle is less than 90 degrees