# Circle Theorems and advice to work out this question-

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#1
So I know that the answer is 65 degrees however how would i write in the answer.
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1 year ago
#2
Well how did you get to that answer?
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#3
(Original post by GabiAbi84)
Well how did you get to that answer?
well ODB equals 25 degrees and so if you construct the other line aswell, it would also be 25 degrees because it is an isosceles triangle
therefore the DOB = 130 degrees. Then i would use the circle theorem : angle at arc = 2x angle at circumference
so 130/2=65 degrees
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1 year ago
#4
(Original post by Randompoggers)
well ODB equals 25 degrees and so if you construct the other line aswell, it would also be 25 degrees because it is an isosceles triangle
therefore the DOB = 130 degrees. Then i would use the circle theorem : angle at arc = 2x angle at circumference
so 130/2=65 degrees
So have you tried writing that?
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#5
(Original post by Muttley79)
So have you tried writing that?
yeah doesnt work
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1 year ago
#6
(Original post by Randompoggers)
yeah doesnt work
You need to write it very formally as Mathswatch is a pain

e.g. angle OBD = 25 [isosceles triangle]
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#7
(Original post by Muttley79)
You need to write it very formally as Mathswatch is a pain

e.g. angle OBD = 25 [isosceles triangle]
i have done my best but im still stuck on 1/4 marks
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1 year ago
#8
(Original post by Randompoggers)
i have done my best but im still stuck on 1/4 marks
Copy exactly what you have written 0
1 year ago
#9
(Original post by Randompoggers)
i have done my best but im still stuck on 1/4 marks
These kind of questions on mathswatch made me waste so many evenings...
My advice is simple, put in your working and answer as you did it and comment on the question your working (if it's one of those where you can comment), explaining to the teacher that MW sucks the major sector. J'ai fini.
1
1 year ago
#10
(Original post by Randompoggers)
danke schon
Cut and paste to this thread what you have written - we can get full marks
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#11
(Original post by Muttley79)
Cut and paste to this thread what you have written - we can get full marks
well ODB equals 25 degrees and so if you construct the other line aswell, it would also be 25 degrees because it is an isosceles triangle
therefore the DOB = 130 degrees. Then i would use the circle theorem : angle at arc = 2x angle at circumference
so 130/2=65 degrees

^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
this is what ive written like before]

also the red lines are added on they are not part of the question.
Last edited by Randompoggers; 1 year ago
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1 year ago
#12
(Original post by Randompoggers)
well ODB equals 25 degrees and so if you construct the other line aswell, it would also be 25 degrees because it is an isosceles triangle
therefore the DOB = 130 degrees. Then i would use the circle theorem : angle at arc = 2x angle at circumference
so 130/2=65 degrees

^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
this is what ive written like before
As I said that is not formal enough - I started you off

OBD = 25 [opposite angles of an isosceles triangle]

angle DOB = 130 [give a reason]

Now carry on like that - you need to do this in the exam 1
#13
(Original post by Muttley79)
As I said that is not formal enough - I started you off

OBD = 25 [opposite angles of an isosceles triangle]

angle DOB = 130 [give a reason]

Now carry on like that - you need to do this in the exam EDO=90 degrees because tangent meets the radius at 90 degrees
OBD is an isosceles triangle so OBD = 25 because base angles on a triangle are equa DOB = 130˚ 180-(25*2)=130
DAB=65˚ because angles subtended at the arc is twice the angle subtended at the circumference so 130÷2=65˚

this is what i have done and it has only given me 2 marks out of 4 , i think i have explained as full as possible now. thank you for the help
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1 year ago
#14
(Original post by Randompoggers)
EDO=90 degrees because tangent meets the radius at 90 degrees
OBD is an isosceles triangle so OBD = 25 because base angles on a triangle are equa DOB = 130˚ 180-(25*2)=130
DAB=65˚ because angles subtended at the arc is twice the angle subtended at the circumference so 130÷2=65˚

this is what i have done and it has only given me 2 marks out of 4 , i think i have explained as full as possible now. thank you for the help
First line is irrelevant - delete it
It's all too wordy

OBD = 25 [reason I gave]

DOB = 130 [angles in a triangle add to 180 - not just a sum you have to give a reason]

DAB = 130/2 = 65 [angle subtended at the centre is twice that subtended by the same arc at the circumference] you missed key words out
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#15
(Original post by Muttley79)
First line is irrelevant - delete it
It's all too wordy

OBD = 25 [reasoni I gave]

DOB = 130 [angles in a triangle add to 180 - not just a sum you have to give a reason]

DAB = 130/2 = 65 [angle subtended at the centre is twice that subtended by the same arc at the circumference] you missed key words out
its okay i got it now 4/4 marks because the mathswatch algorithm is so terrible you have to get a word for word answer.
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1 year ago
#16
(Original post by Randompoggers)
its okay i got it now 4/4 marks because the mathswatch algorithm is so terrible you have to get a word for word answer.
Reasons are expected in GCSE answers - you did not give reasons for the 130 you just did the calculation without any justification - you must state which theorem you are using.
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1 year ago
#17
(Original post by Randompoggers)
its okay i got it now 4/4 marks because the mathswatch algorithm is so terrible you have to get a word for word answer.
What did you put eventually?
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1 year ago
#18
What did u write???
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