Circle Theorems and advice to work out this question-

Randompoggers

So I know that the answer is 65 degrees however how would i write in the answer.

Reply 1

GabiAbi84

Well how did you get to that answer?
What was your first step?

Reply 2

Randompoggers

Original post by GabiAbi84

Well how did you get to that answer?
What was your first step?

Reply 3

Muttley79

Original post by Randompoggers

So have you tried writing that?

Reply 4

Randompoggers

Original post by Muttley79

So have you tried writing that?

yeah doesnt work

Reply 5

Muttley79

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]

Reply 6

Randompoggers

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

Reply 7

Muttley79

Original post by Randompoggers

i have done my best but im still stuck on 1/4 marks

Copy exactly what you have written :smile:

Reply 8

Da14a

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.

Reply 9

Muttley79

Original post by Randompoggers

danke schon

Cut and paste to this thread what you have written - we can get full marks

Reply 10

Randompoggers

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.

(edited 3 years ago)

Reply 11

Muttley79

Original post by Randompoggers

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 :smile:

Reply 12

Randompoggers

Original post by Muttley79

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

Reply 13

Muttley79

Original post by Randompoggers

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

Reply 14

Randompoggers

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.

Reply 15

Muttley79

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.