Find angle of a triangle with given sides

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To find angle B in triangle ABC with sides AB=7, BC=8, and CA=9, the cosine rule is applied. The calculation involves using the formula cos B = (a² + c² - b²) / (2ac), where a, b, and c are the lengths of the sides. The result is approximately 73.4 degrees when rounded to three significant figures. A calculator is necessary to compute the cosine value accurately. Understanding the cosine rule is essential for solving triangle problems effectively.
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In a triangle ABC, AB=7, BC=8, CA=9, find angle B correct to 3 significant figures.
The answer is 73.4, but i don't know how to calculate it, thanks.
 
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Use the cosine rule.
 
U'll need a calculator to compute B,i.e.solve the equation

\cos B=value

and select the first 3 decimals the calculator shows u...

Daniel.
 
O, I forgot there is a rule called " cosine rule" in the world, thanks.
 
The world hath many rules, none of which you ought to ignore..:wink:
 
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