a²=b²+c²-2bcCosA
a²= 4²+ý²-2(4)(y)Cos66
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Answer:
As we have ABC is a triangle hence
a
+
b
+
c
=
0
So,
a
+
b
=−
c
Squaring on both sides,
(
a
+
b
)(
a
+
b
)=(−
c
)(−
c
)
b
2
+a
2
+2abcos(π−C)=c
2
[Using dot product ]
b
2
+a
2
+2ab(−cosC)=c
2
c
2
=a
2
+b
2
−2abcosC
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