Find the Value of Angle D in this Triangle | Fast & Easy Explanation

[philipkudrna]

Before watching: 110 degrees. 180-40=140 (sum of other two angles). Half is 70. Therefore the missing angle is 180-70=110 degrees.

[Aryan_Giri]

Actually 'D' is incentre of ∆ABC and the angle at incentre is 90+1/2 of corresponding angle.

[reiniernn]

10 seconds puzzle....Triangle has 180 degrees angle (total). A=40. B+C =140 together. Both, B and C, are cut in 2 equal halves. Those halves together ar 70 degrees. Also triangle BCD is 180 degrees total...D = 180-70=110.

[annatygrys]

I solved it in my mind within 30 seconds. Greetings!

[alexrocha]

Good Morning Master
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Congratulations

[sagarreddy]

Thank you sir. It is more useful for me

[devondevon]

Can be done without geometry. let C=2p and B=2n (since there are two ps and two ns)
then 40 + 2p + 2n =180
2p + 2n= 140
2 (p + n) =140
p+n = 70
Therefore D =110 (as 110 + 70=180)
as said if A was 30 then D would =105, if A was 20 D would =100, if A was 50, then D would =115, if A 60
D=120 . Notice that every time A increases by 10 D goes up by 5.

[AnonimityAssured]

With so little information provided, we can safely assume that the actual angles at B and C don't matter. Therefore, we can simply choose an abitrary angle for one of them, which will quickly yield the correct answer. That's the quick and dirty way. The general result of a more rigorous study is: D = (180 + A)/2 (all angles in degrees).

[devondevon]

Answer 110
didn't use geometry but logic as angle A will determine D, if angle A is 30 D is 105 if A is 20 D is 100

[JSSTyger]

I like to pause these videos at the start to see if I can get the answer.
= 40+2α+2ß, and thus α+ß = 70
α+ß+D = 180, and thus D = 110

[mustafizrahman]

I have solved it in only 2 seconds. ( It's really true.) The answer is 110 degrees. I have seen the triangle and guessed what type of question it is. I have also known that ANGLE BDC= 90+A/2.

[shreemathematicstutorials]

Angle bisectors make point D as Incentre of the Triangle...So formula is angle D = (90 + A/2)

[kiranbarnwal]

110 degree correct answer
Nice question👍

[StevenTorrey]

I would have just divided the 70 degrees in half, so 35 + 35 = 180 = --so Angle d = 110 degrees. Or something like that.

[forexstrategies]

I'm in 9th standard and I have solved it in less than 50 seconds.

[colew]

The real question I have is how do you find what a equals and what b equals

[nicholas_smpbm]

Thx but I already know how to solve before explain

[theophonchana]

theta + alpha + beta = 180°
theta + 70° = 180°
theta = 110°

[Teamstudy]

Ans /D = 110 degree (Solved in around 3 second)