Maths help Needed Part 2 x.x URGENT >.<

jlzk SG

Addtional information:A,B,C,D lie on the circle,Center O

AOD 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

jlzk SG

Any kind soul can help . urgent x.x

iamapebble SG

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 z

Since OBD is a isoceles triangle,
Angle OBD = x = 20 degrees

Given OB // DC,
z = 20 degrees [alternate angles]

jlzk SG

Blank-

Oceane SG

Addtional information:A,B,C,D lie on the circle,Center O

AOD Diameter ,OB parallel to DC

BOD=140 degree

Find the unknowns,

Y degree

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)

jlzk SG

X = Z because of the alternate angles theory. OB // DC.

OBD = BDO = 20 (isoceles triangle)
CDB = OBD = 20 (alternate angles)

Understood! Thanks!

jlzk SG

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

iamapebble SG

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

jlzk SG

Tons of thanks!!! But if there is example pls do show den i can reinforce in my brain x.x Sorry to trouble you!

jlzk SG

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!

jlzk SG

Once again tons of thanks iamapebble & Oceane =)

iamapebble SG

No problem :) and good luck~