Answer:
Length of third side = 30 inches
Explanation:
We will need a system of equations to find the length of the third side.
First equation:
- Let x represent the length of just one of the congruent sides and let y represent the length of the third side.
We know the perimeter of a triangle is simply the sum of its sides.
Thus, since the perimeter is 45, our first equation is x + x + y = 45, which simplifies to 2x + y = 45.
Second equation:
Since we're told that the length of the third side is twice as long as the sum of the congruent sides, our second equation is y = 2(x + x), which simplifies to y = 2(2x) and then finally y = 4x
Method: Substitution.
We can first solve for x (length of one of the congruent sides) by substituting y = 4x for y in 2x + y = 45:
2x + 4x = 45
6x = 45
x = 7.5
Find y:
Now we can find y (length of the third side) by plugging in 7.5 for x in y = 4x:
y = 4(7.5)
y = 30
Thus, the length of the third side is 30 inches.
Optional Step to check validity of answers.
First equation: Check that the sum of 7.5, 7.5, and 30 = 45
7.5 + 7.5 + 30 = 45
15 + 30 = 45
45 = 45
Second equation: Check that 30 is twice the sum of 7.5 + 7.5
30 = 2(7.5 + 7.5)
30 = 2(15)
30 = 30
Thus, our answers are correct and we've correctly determined the length of the third side of the triangle in inches.