A) \[{{c}^{2}}={{a}^{2}}+{{b}^{2}}+ba\]
B) \[{{c}^{2}}={{a}^{2}}+{{b}^{2}}-ba\]
C) \[{{c}^{2}}={{a}^{2}}+{{b}^{2}}-2ba\]
D) \[{{c}^{2}}={{a}^{2}}+{{b}^{2}}+2ba\]
E) None of these
Correct Answer: A
Solution :
Explanation Option [a] is correct. \[\cos \,C=\frac{{{a}^{2}}+{{b}^{2}}-{{c}^{2}}}{2ab}\] \[-\frac{1}{2}=\frac{{{a}^{2}}+{{b}^{2}}-{{c}^{2}}}{2ab}\] \[\Rightarrow {{c}^{2}}={{a}^{2}}+{{b}^{2}}+ab\]
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