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Abc is a Triangle in Which ∠A — 72°, the Internal Bisectors of Angles B and C Meet in O. Find the Magnitude of ∠BOC - Mathematics

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Question

ABC is a triangle in which ∠A — 72°, the internal bisectors of angles B and C meet in O.
Find the magnitude of ∠BOC.

Solution

 

Given, 

ABC is a triangle 

`∠ A=72^@` and internal bisector of angles B and C meeting O 

In` Δ ABC = ∠ A+∠ B+∠ C=180^@` 

⇒`72^@+∠ B+∠ C=180^@` 

⇒`∠ B+∠C =180^@-72^@ ` divide both sides by ‘2’ 

⇒`∠ B/2+∠ C/2=108^@/2`              ..................(1) 

⇒`∠ OBC +∠ OCB =54^@`             ...................(1) 

Now in `Δ BOC⇒ ∠OBC +∠ OCB +∠ BOC    = 180^@` 

⇒ `54^@+∠BOC=180^@` 

⇒ `∠BOC=180^@-54^@=126^@` 

∴`  ∠ BOC=126^@`

 

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Chapter 11: Triangle and its Angles - Exercise 11.1 [Page 10]

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RD Sharma Mathematics [English] Class 9
Chapter 11 Triangle and its Angles
Exercise 11.1 | Q 8 | Page 10
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