If a bar + b bar = c bar and c= root over a square + b square then angle between a bar and c bar About the author Delilah
Correct option is D 60 ∘ Given a ˉ + b ˉ + c ˉ =0 and ∣ a ˉ ∣=3,∣ b ˉ ∣=5,∣ c ˉ ∣=7 Let angle between a ˉ and b ˉ be θ a ˉ + b ˉ + c ˉ =0 ⇒ a ˉ + b ˉ =− c ˉ ⇒∣ a ˉ ∣ 2 +∣ b ˉ ∣ 2 +2 a ˉ ⋅ b ˉ =∣ c ˉ ∣ 2 ⇒9+25+30cosθ=49 ⇒cosθ= 2 1 ∴θ= 3 π Hence, option D. Reply
Correct option is
D
60
∘
Given
a
ˉ
+
b
ˉ
+
c
ˉ
=0 and ∣
a
ˉ
∣=3,∣
b
ˉ
∣=5,∣
c
ˉ
∣=7
Let angle between
a
ˉ
and
b
ˉ
be θ
a
ˉ
+
b
ˉ
+
c
ˉ
=0
⇒
a
ˉ
+
b
ˉ
=−
c
ˉ
⇒∣
a
ˉ
∣
2
+∣
b
ˉ
∣
2
+2
a
ˉ
⋅
b
ˉ
=∣
c
ˉ
∣
2
⇒9+25+30cosθ=49
⇒cosθ=
2
1
∴θ=
3
π
Hence, option D.