Is this the correct way to present a Cambridge O Level geometry solution?
Hi everyone,
I’m trying to solve this geometry question and also wondering if my working format is acceptable for Cambridge O Level exams. This is not for homework. I'm trying to learn this for my mathematics o levels. i just want to know if this format is correct or not.
question:
ABCD is a parallelogram. E is a point on AB and EC = BC. Angle ECB = 40° and angle DEC = 60°. Find the value of x.
My solution:
Triangle ECB has EC = BC ∴ base angles are equal
Let base angles = x
x + x + 40 = 180 2x + 40 = 180 2x = 140 x = 70°
∠EBC = 70°
Since E lies on AB, ∠EBC = ∠ABC ∴ ∠ABC = 70°
Opposite angles in a parallelogram are equal ∴ ∠ADC = 70°
In triangle DEC: 70 + 60 + x = 180 130 + x = 180 x = 50°
Is this step-by-step method and notation acceptable for Cambridge O Level marking? And is my reasoning correct?
Thanks!