Q. 4
In a ∆ABC, if a = 18, b = 24, c = 30, find cos A, cos B and cos C.
Answer :
Note: In any ΔABC we define ‘a’ as length of side opposite to ∠A , ‘b’ as length of side opposite to ∠B and ‘c’ as length of side opposite to ∠C .
Key point to solve the problem:
Idea of cosine formula in ΔABC
• 
Cos A = 
• Cos B = 
• Cos C = 
As we have a = 18, b = 24 and c = 30
∴ Cos A = 
Cos B = 
Cos C = 
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