© examsiri.com
Question : 26 of 120
Marks:
+1,
-0
Solution:
We have
a+b+c=0 ⇒b+c=−a ⇒|b+c|=|−a| ⇒|b+c|=|a| ⇒|b+c|2=|a|2 ⇒‌‌(b+c)⋅(b+c)=|a|2 ⇒‌‌|b|2+|c|2+2|b||c|cos‌θ=|a|2
⇒‌‌(5)2+(3)2+2×5×3‌cos‌θ=(7)2
⇒‌‌25+9+30‌cos‌θ=49 ⇒‌‌30‌cos‌θ=15 ⇒‌‌cos‌θ=‌ ⇒‌‌θ=60∘ or
∴ Angle between
b and
c is
‌
© examsiri.com
Go to Question: