Maths help Needed Part 2 x.x URGENT >.<
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Addtional information:A,B,C,D lie on the circle,Center OAOD Diameter ,OB parallel to DC
BOD=140 degree
Find the unknowns,
Y degree
Finding of y degree i though its 70 degree cause angle of the center is twice the angle at the circumference but how come the ans key put not 70 x.x if i am wrong can some kind soul kindly correct me.
X/Z degree
How can i tell if x and z degree is equal ? As the line BD just cut through x.x
Fore Thanks =p
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Any kind soul can help . urgent x.x
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Finding y
Yes, you are right, angle at center is twice angle at circumference, but this applies for corresponding angles, which means, they must be facing the same side. =)
Therefore from this question,
Reflex Angle BOD = 2y
(360 - 140) = 2y
y = 110 degrees.Finding x
x = (180 - 140) / 2
= 20 degrees [OB = OD = radius of circle, isoceles triangle]
Finding zSince OBD is a isoceles triangle,
Angle OBD = x = 20 degrees
Given OB // DC,
z = 20 degrees [alternate angles] -
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Originally posted by jlzk:
Addtional information:A,B,C,D lie on the circle,Center OAOD Diameter ,OB parallel to DC
BOD=140 degree
Find the unknowns,
Y degree
Finding of y degree i though its 70 degree cause angle of the center is twice the angle at the circumference but how come the ans key put not 70 x.x if i am wrong can some kind soul kindly correct me.
X/Z degree
How can i tell if x and z degree is equal ? As the line BD just cut through x.x
Fore Thanks =p
X = Z because of the alternate angles theory. OB // DC.OBD = BDO = 20 (isoceles triangle)
CDB = OBD = 20 (alternate angles) -
Originally posted by Oceane:
X = Z because of the alternate angles theory. OB // DC.OBD = BDO = 20 (isoceles triangle)
CDB = OBD = 20 (alternate angles)Understood! Thanks!
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Originally posted by iamapebble:
Finding y
Yes, you are right, angle at center is twice angle at circumference, but this applies for corresponding angles, which means, they must be facing the same side. =)
Can explain abit on that and provide some examples if possible cause i cant really visualise wad u said.Sorry x.x
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Facing same side meaning in literal terms, like you see angle BCD is facing downwards, so the angle of BOD must be reflex because only the reflex of BOD is facing downwards. (: This has to be in your thought process though. You don't have to explain in your working, just simply angle at centre = 2angles at circumference.
Look at this diagram,
O is the centre so we have:
Angle AOB (x+y) = 2 Angles at ACB = 2(a+b)
Notice that they are both facing downwards?Image credit: http://www.mathsteacher.com.au/year10/ch06_geometry/08_angle_at_centre/circ.htm
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Originally posted by iamapebble:
Facing same side meaning in literal terms, like you see angle BCD is facing downwards, so the angle of BOD must be reflex because only the reflex of BOD is facing downwards. (: This has to be in your thought process though. You don't have to explain in your working, just simply angle at centre = 2angles at circumference.
[edit] Let me try finding examples =)Tons of thanks!!! But if there is example pls do show den i can reinforce in my brain x.x Sorry to trouble you!
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Originally posted by iamapebble:
Look at this diagram,
O is the centre so we have:
Angle AOB (x+y) = 2 Angles at ACB = 2(a+b)
Notice that they are both facing downwards?Image credit: http://www.mathsteacher.com.au/year10/ch06_geometry/08_angle_at_centre/circ.htm
Saw i think roughly get the idea lers!
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Once again tons of thanks iamapebble & Oceane =)
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No problem :) and good luck~