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In the figure, find angle(DAB), given angle(DBA)=50 and angle(BCA)=70.

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In the figure, find angle(DAB), given angle(DBA)=50 and angle(BCA)=70. [#permalink]

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In the figure, find angle(DAB), given angle(DBA)=50 and angle(BCA)=70.

a) 50
b) 60
c) 70
d) 40
[Reveal] Spoiler: OA

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Re: In the figure, find angle(DAB), given angle(DBA)=50 and angle(BCA)=70. [#permalink]

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New post 09 Jun 2011, 20:25
b for me --60 degrees

Consider the intersection of line AC and BD as O. Angle ADB should be equal to angle BCA (inscribed angles)

So DAB = 180 - angle ADB - angle DBA = 180 - 70 - 50 = 60 degrees

OA??
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Re: In the figure, find angle(DAB), given angle(DBA)=50 and angle(BCA)=70. [#permalink]

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New post 10 Jun 2011, 10:49
In the Figure
Given - DBA = 50
BCA = 70

Now angle BCA = BDA
BDA = 70

In triangle ADB
BDA + DBA + DAB = 180
Hence DAB = 60
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Re: In the figure, find angle(DAB), given angle(DBA)=50 and angle(BCA)=70. [#permalink]

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Re: In the figure, find angle(DAB), given angle(DBA)=50 and angle(BCA)=70. [#permalink]

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New post 25 Mar 2016, 22:10
angle(DBA)=50 and angle(BCA)=70

Using Property Angle(BCA) = Angle (BDA) =70
angle DAB= 180-70-50=60
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Re: In the figure, find angle(DAB), given angle(DBA)=50 and angle(BCA)=70. [#permalink]

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New post 04 Apr 2016, 13:38
Here we need to use the property that a chord suspends equal inscribed angles => AB is the chord so <DAB => 180-(70+50) => 60
hence B
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Re: In the figure, find angle(DAB), given angle(DBA)=50 and angle(BCA)=70. [#permalink]

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New post 20 Aug 2017, 08:30
I do not understand how the OA is reached. Do we have to assume that because the angles look the same in the picture that they are the same value? We are not given any details in the question.
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In the figure, find angle(DAB), given angle(DBA)=50 and angle(BCA)=70. [#permalink]

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New post 20 Aug 2017, 11:50
EwokBanshee wrote:
I do not understand how the OA is reached. Do we have to assume that because the angles look the same in the picture that they are the same value? We are not given any details in the question.

EwokBanshee
No, don't assume values from similar appearance. :-)

The posters are relying on properties of circles and inscribed angles, about which you can read in the excellent GMATCLUB Math Book. I've linked to the particular section on circles for you, below.

The language can be very technical at times. If you get stuck, check other sites with a search engine and search terms "incribed angle circles." (No quotation marks. They're for clarity in my sentence.)

Hope it helps.

Circles, https://gmatclub.com/forum/math-circles-87957.html
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In the figure, find angle(DAB), given angle(DBA)=50 and angle(BCA)=70.   [#permalink] 20 Aug 2017, 11:50
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