13. If A=(1, 1, 1), B=(1, 2, 3), C=(2, -1, 1) be the
vertices of a A ABC, then the length of the
internal bisector of the angle 'A' is
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Answer:
Given:AB=AC
In triangle ABC
cosc=
2AC.BC
AC
2
+BC
2
−AB
2
=
2AC.BC
BC
2
=
2AC
BC
→i
In △ADC
cosC=
2AC.DC
AC
2
+DC
2
−AD
2
→ii
I and ii
2AC
BC
=
2AC.BC
AC
2
+DC
2
−AD
2
⇒BC.DC=AC
2
+DC
2
−AD
2
(BD+DC)DC=AB
2
+DC
2
−AD
2
=BD.DC=AB
2
−AD
2
solution sorry if wrong❌
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