# Find the perimeter of a triangle if its sides are 7 and 15 cm and form an angle of 60 degrees.

July 26, 2021 | education

| Knowing the lengths of the two sides of the triangle and the angle between them, we determine the length of the third side using the cosine theorem for a triangle.

AB ^ 2 = AC ^ 2 + BC ^ 2 – 2 * AC * BC * Cos60 = 225 + 49 – 2 * 15 * 7 * 1/2 = 274 – 105 = 169.

AB = 13 cm.

Let’s define the perimeter of the triangle ABC.

Ravs = AB + BC + AC = 13 + 7 + 15 = 35 cm.

Answer: The perimeter of triangle ABC is 35 cm.

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