Find the length of the third side of a triangle with a perimeter of 21 in. if the sum of the other two is 15 in.
Set up and equation and solve
Let the length of the third side be x inches.
We are given that the perimeter of the triangle is 21 in, so we can set up the equation:
x + (sum of the other two sides) = 21
x + 15 = 21
Subtracting 15 from both sides, we have:
x = 6
Therefore, the length of the third side is 6 inches.
Let's assume the length of the third side of the triangle is "x".
According to the given information, the perimeter of the triangle is 21 inches, which means the sum of all three sides is 21 inches.
So, we can set up an equation:
x + (one side) + (other side) = 21
We are given that the sum of the other two sides is 15 inches. Therefore, we can substitute 15 for "(one side) + (other side)" in the equation:
x + 15 = 21
To solve for x, we can subtract 15 from both sides of the equation:
x = 21 - 15
x = 6
Therefore, the length of the third side of the triangle is 6 inches.