Question

The lengths of two sides of a triangle are 2x² - 10x + 6 inches and x²-x-4 inches. If the perimeter of the triangle is 3x² - 7x + 2 inches, find the length of the third side.

[Hint: draw and label a picture]​

Answer 1

Length of third side = 4x inches

Explanation:

The perimeter of a triangle is the sum of the lengths of its three sides.

Step 1: First we need to add the two sides we have and simplify:

2x^2 - 10x + 6 + x^2 - x - 4

(2x^2 + x^2) + (-10x - x) + (6 - 4)

3x^2 - 11x + 2

Step 2: Now, we need to subtract this from the perimeter to find the length of the third side:

Third side = 3x^2 - 7x + 2 - (3x^2 - 11x + 2)

Third side = 3x^2 - 7x + 2 - 3x^2 + 11x - 2

Third side = 4x

Thus, the length of the third side is 4x inches

Optional Step 3: We can check the validity of our answer by seeing if the sum of the lengths of the three sides equals the perimeter we're given

3x^2 - 7x + 2 = (2x^2 - 10x + 6) + (x^2 - x - 4) + (4x)

3x^2 - 7x + 2 = (2x^2 + x^2) + (-10x - x + 4x) + (6 - 4)

3x^2 - 7x + 2 = 3x^2 + (-11x + 4x) + 2

3x^2 - 7x + 2 = 3x^2 - 7x + 2

Thus, we've correctly found the length of the third side.

I attached a picture of a triangle that shows the info we're given and the answer we found.