Answer:
Perimeter = 15
Explanation:
We are told that the length of each of the 3 sides of the triangle are consecutive odd integers.
Thus means that we can write the 3 terms as;
(x - 2), x, (x + 2)
Thus, perimeter is;
P = (x - 2) + x + (x + 2)
P = 3x
If an angle is 120°, it means that the corresponding side that is directly opposite the angle is the largest side of the triangle.
Thus, this side is (x + 2)
Using cosine rule, we have;
(x + 2)² = x² + (x - 2)² - 2(x(x - 2))cos 120
Expanding, we have;
x² + 4x + 4 = x² + x² - 4x + 4 - (2x² + 4x)(-½)
This reduces to;
4x = x² - 4x + x² - 2x
2x² = 10x
2x = 10
x = 10/2
x = 5
Thus, other sides are;
(x - 2) = 5 - 2 = 3
And (x + 2) = 5 + 2 = 7
So,perimeter is;
P = 3x = 3 × 5 = 15