Given points A (1: 1), B (4: 1), C (4: 5), find the cosines of the triangle ABC.

univerkov | November 30, 2020 | education

find the length AB:
AB = √ ((4-1) square + (1-1) square) = 3
similarly the rest:
BC = 4
AC = 5
by the cosine theorem:
25 = 25-50 * сosB
COSB = 0
angle B = 90 degrees
9 = 25 + 16 – 2 * 4 * 5 * COSC
COSC = 32/40 = 4/5
16 + 25 + 9 – 2 * 3 * 5 * COSA
COSA = 18/30 = 9/15

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