# Pre-Calculus

posted by .

∏ <-- 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
2*180/∏ = 114.59

^Ive no idea how she got that :S

• Pre-Calculus -

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.

• Pre-Calculus -

Thanks so much :)

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