can someone help with this geometry question

[almostdonewithschooling]

can someone help or have solution to this?

i tried pythagoras but it doesnt work cause its not a right angle. also the answer is 72 degree, not sure if thats wrong or what

thank you

[AngelWings]

You’re right to consider this as a triangle. I’ll give you a hint: consider the angle being at the centre of a triangle in a regular polygon. Do you know of any formulas that relate to this scenario?

(Extra hint: This formula was also similar to the one used for the 50c question in the VCAA 2015 exam - VCAA 2015 E1 Geometry module Q7.)