The partial circles in each corner mean that all 3 angles are identical, which means this is an equatorial triangle. In an equatorial triangle all three sides are the same.
We can set two of the equations to equal each other and solve for x:
3x -5 = 2x +20
Add 5 to each side:
3x = 2x +25
Subtract 2x from each side:
x = 25
Google on the word SCALAR. that's the word your looking for
If you have a calculator, you can use the inverse cos " cos⁻¹ " key. Many upper level books write that as Arccos so as not to confuse you with a negative exponent. We do that because if you take the cosine of any angle, and then the inverse cosine of any angle, it leads you back to the original angle. Think of it as a big "UNDO" button.
To one decimal place, that result is 61.6 degrees.
