In Fig. the sides AB and AC of ∆ABC are produced to points E and D respectively. If bisectors BO

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class 9 chapter 6
lines and angles extra question
Example 8 : In Fig. the sides AB and AC of
∆ABC are produced to points E and D respectively.
If bisectors BO and CO of ∠ CBE and ∠ BCD
respectively meet at point O, then prove that
∠ BOC = 90°–1/2
∠BAC.

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◾Deepak Rajoria
(Maths Teacher)
◾Focus Classes - Class 9, Class 10, Maths

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[gamoboy]

Tommorow is my exam and I see this video thanks

[NMJS]

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[shininglightingfantomfight]

Thank you so much sir, your explanation is too good 😊

[usedtobejosh_dinkshotst_t]

Sir, this was impeccable. This is the best explanation I've ever listened to...

[shivanshverma]

Thanks sir you are best sir app abb tak ke best teacher

[alster]

Very easy

We let

ABC = a1 and ACB = a2
OBC= a3 and OCB = a4


By Exterior Angle Theorem we get
A+a1= DCB

Halving both sides we get

(A+a1)/2= DCB/2

But DCB/2 = a4

So (A+a1)/2 = a4

By Exterior Angle Theorem again, we have

A+a2= EBC

Same process, halving both sides we have

(A+a2)/2 = EBC/2

But EBC/2 = a3

So (A+a2)/2= a3

Going to Triangle BOC, we have


a3+a4+BOC=180


By substitution we have

(A+a1+A+a2)/2+BOC =180

By using the interior angles of Triangle BAC

We have A+a1+a2= 180

Substituting this to Triangle BOC we have

(A+180)/2+BOC=180

Breaking down the left side we gave

A/2+90+BOC=180

Solving further, we have proven that

BOC= 90-A/2

[ananyagupta]

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[Monika_Sangal]

I have checked full youtube but then I find your video sir. Great explaination❤

[akshit]

Thank you so much sir just thank you so very much

[gleamgirlvlog]

Today's my test I hope to get full marks

[pabitramandal]

Sir I would request you not to put the background music, you were explaining so good and the background music keeps interrupting 😂 . You deserve a lot more sir loved your explanation after watching your videos my maths teacher feels he is useless, you explained so good 👍🏻

[allinonechannel]

Thank you so much sir. I was not able to understand this question but now i am able to solve it very efficiently and perfectly and easily.

[lenovo]

Very helpful thank you so much sir 👍👍👍🙏🙏🙏

[spicymark]

I was not able to understand this topic for ages but sir apne bataya to sab ekdum samaj aagaya thank you sir

[rtgaming]

Sir you explaination is just mind blowing 😇😇

[amishkhurana]

kya sikhate ho sir sab samajh mein aa gaya thank u very much

[anshumanyadav]

Tomorrow is my final exam I see at 12:00 am

[pragatipawadsheety]

Sir why u took angle a +b +c=180 degree reason

[admotivation]

Thanks sir for your this great explanation