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# In triangle ABC, we have ab=5, bc= 8 and ac=7, as shown below:

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In triangle ABC, we have ab=5, bc= 8 and ac=7, as shown below:

Calculate

$$\cos (\angle A), \cos (\angle B), \cos (\angle C)$$

and enter them in that order.

Apr 13, 2022

#3
+33151
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Use the Cosine rule: $$\cos A = \frac{b^2+c^2-a^2}{2bc}$$

Here:  a = 8, b = 7, c = 5

Cycle a, b and c for the other angles.

Apr 13, 2022
#4
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Hello, how whould I get cosb and c then?

Apr 13, 2022
#5
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For cos B change the formula so that A → B, a → b, b → c, c → a

See if you can then work out what to do for cos C.

Alan  Apr 13, 2022