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primary 5 | Maths | Angles & Geometry
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Mandy
Mandy

primary 5 chevron_right Maths chevron_right Angles & Geometry chevron_right Singapore

Pls assist. Tks

Date Posted: 11 months ago
Views: 154
Phylicia Tong
Phylicia Tong
11 months ago
The answer of 23 degrees is correct.
Mak, Ivan
Mak, Ivan
11 months ago
Hi Phylicia, that's great!
Just a note, be careful that your concept of ∠ACB=∠ACD is incorrect ∠ACB and ∠ACD cannot be assumed to be the same even though triangle BCD is an isosceles. Please note! :)
Triangle BCD is an isosceles, that means that BC = CD and ∠DBC = ∠BDC only!
After looking, try working it out. It helps!

Cheers,
Ivan
Phylicia Tong
Phylicia Tong
11 months ago
Haha Ivan, can perceive you are very enthusiastic. I tutor secondary sch maths so this is a cinch ;)
Mak, Ivan
Mak, Ivan
11 months ago
@Phylicia: Oh hey! I mistook you for the original poster, Mandy. So you teach too. Where're you from?

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Mak, Ivan
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Mak, Ivan
Mak, Ivan
11 months ago
Just a note, be careful that your concept of ∠ACB=∠ACD is incorrect Please note! :)
Triangle BCD is an isosceles, that means that BC = CD and ∠DBC = ∠BDC only!
Mak, Ivan
Mak, Ivan
11 months ago
I'm sorry @Ms Jaslyn Lim, but your answer ∠BDC = 53 degrees is not correct.
We know that triangle ACB is an equilateral triangle, i.e. AB= AC= BC and triangle BCD is an isosceles triangle, i.e. BC=CD.
Hence we know that AC = CD. That is, ACD is an isosceles triangle (triangle with two equal sides is ALWAYS an isosceles). i.e. ∠DAC = ∠ADC = 53 degrees.
Hence ∠ACD = 180-53-53=74 degrees.
∠DBC = BDC = (180-60-74)/2=23 degrees.
I have mathematical proofing for my answer. Can you show proof for your answer?