Using synthetic division, how do you know if a given value is a root of a polynomial function?

What is the area of the triangle 10 13 12

The lengths of all sides of a triangle are integers when measured in decimeters. one of the sides has length of 1 dm and another of 3 dm. find the perimeter of the triangle.'

Lucy is a dress maker. she sews \dfrac47 7 4 ? of a dress in \dfrac34 4 3 ? hour. lucy sews at a constant rate. at this rate, how many dresses does lucy sew in one hour? include fractions of dresses if applicable.