PreCalculus
posted by Shreya on .
Trigonometric Functions, Radian Measure
∏ < will be using this for pi
Using exact values, convert to radians ( hint use fraction of ∏)
90° = 90°*∏/180° = 1∏/2
^^would it be right to also call it 2∏ radians?
Determine the angle at the centre of the circle, radius 6cm, for each arc length.Express each angle in radians and then in degrees.
3cm
a = rθ
3 = 6θ
1/2 = θ
1/2*180°/∏
=28.6°
^One of my friends got a totally different answer, and she got
θ = 2 rad
2*180/∏ = 114.59
^Ive no idea how she got that :S

It is obvious she is wrong.
the whole circumference of a 6cm circle is 12pi or about 36 cm
3cm is about 1/12 of the whole, or 1/12 of 360° = 30°
she obviously confused the formula.
ALWAYS do a general sanity check on your answers. Just because you get a value doesn't mean that it's correct. 
Thanks so much :)