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Question : 28 of 160
Marks:
+1,
-0
Solution:
‌‌‌(b+c)‌cos‌A+(c+a)‌cos‌B+(a+b)‌cos‌C
‌=b‌cos‌A+c‌cos‌A+c‌cos‌B+a‌cos‌B+a‌cos‌C+b‌cos‌C
‌‌=(b‌cos‌C+c‌cos‌B)+(c‌cos‌A+a‌cos‌C)+(a‌cos‌B+b‌cos‌A)
Using projection formula,
‌a=(b‌cos‌C+c‌cos‌B)
‌b=(c‌cos‌A+a‌cos‌C)
‌c=(a‌cos‌B+b‌cos‌A)
Substituting above values in Eq. (i), we get
‌a+b+c
‌‌ Thus, ‌(b+c)‌cos‌A+(c+a)‌cos‌B+(a+b)‌cos‌C
‌=a+b+c
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