This isosceles triangle has two sides of equal length , a, that are longer than the length of the base , b. the perimeter of the triangle is 15.7 cm. the equation 2a + b = 15.7 models this information. if one of the longer sides is 6.3 cm, which equation can be used to find the length of the base ?

We are give the equation of the perimeter of the triangle as follows:
2a + b = 15.7 
where b represents the base.

Now, if we want to calculate the length of the base, all we have to do is isolate the b in one side of the equation as follows:
b = 15.7 - 2a

We know that a = 6.3 cm, therefore, the length of the base can be calculated as follows:
b = 15.7 - 2(6.3) = 3.1 cm