In a right-angled triangle, the ratio of the adjacent leg to its hypotenuse is called the cosine of the angle.
By condition, in triangle ABC, angle C = 90 °, hypotenuse AB = 35 cm, opposite leg
BC = 28 cm.Using the Pythagorean theorem, we find the adjacent leg AC:
| AC | = √ (| AB | ^ 2 – | BC | ^ 2) = √ (35 ^ 2 – 28 ^ 2) = √ (1225 – 784) = √441 = 21.
Now we calculate cos A = 21/35 = 0.6.
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