# The sides of the triangle are 3 cm, 5 cm, and 7 cm. Find the corner of the triangle opposite to the side equal to 7 cm.

October 1, 2021 | education

| Cosine solution:

Cosine theorem: a2 = b2 + c2 – 2bccosα.

Instead of letters, we substitute numbers and it turns out:

7 ^ 2 = 3 ^ 2 + 8 ^ 2-2 * 3 * 8cosα.

49 = 9 + 64-48cosα

49 = 73-48cosα

49-73 = -48cosα

-48cosα = -24

cosα = 0.5

α = 60 °

Answer: the angle of the triangle of the opposite side is α = 60 °

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