If the largest angle of a triangle is 120° and it is included between sides of 1.5 and 0.5, then to the nearest 10th the largest side of the triangle is what?

Just apply the cosine law:

Let AB, be the side opposed to the angle 120°

AB² = (05) ² + (1.5) ² - 2 (0.5) (1.5). cos (120°). But we know that cos (120°) = - 1/2

Then:

AB² = 0.25 + 2.25 + 0.75

AB² = 3.25

And AB = √3.25 = 1.8