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### Course: Class 10 (Old)>Unit 11

Lesson 1: Perimeter of circular figures

# Angles, arc lengths, and trig functions — Harder example

Watch Sal work through a harder Angles, arc lengths, and trig functions problem.

## Want to join the conversation?

• how did sal know that the opposite side of the 30 degree angle was 1/2 of the radius?
• The 30 degree angle forms a 30-60-90 right triangle, which has special ratios between its side lengths. If the side opposite from 30 is x, the side opposite 60 is x*sqrt(3) and the side opposite 90 (hypotenuse) is 2x. We want to find the sine of the 30 degree angle. The sine of an angle tells us the ratio of the opposite to the hypotenuse in its associated right triangle. We know that the opposite side is 1/2 of the hypotenuse since the opposite side is x and hypotenuse is 2x, so sin(30) = 1/2.
• which calculator is more recommended scientific or graphic?
for SAT 1
• All the questions on the SAT can be solved using a scientific or graphing calculator. There are no such question on the SAT 1 which can be only solved using a graphing calculator. Still, if you want you can take a graphing calculator to the test if you think that it will help you score more.
• why do you multiply 260/360 and 10pi
• 10pi is the entire circumference. 260/360 is the fraction that represents the segment of the arc, because the angle is 260 degrees out of a total 360 degrees. Basically, x is 260/360ths of the entire circumference, so you multiply the fraction by the whole to find the length of the arc, or the portion of the circumference. OR, there's a formula you use to find arc length. It's `code`
``(x/360) * C``
where x is the measure of the central angle and C is your circumference. Hope that helps!
• x=rcosθ
y=rsinθ
you know both r and θ
and done!
• im appearing for the digital SAT on 11th March. are the foundation vids of every topic enough prep?
• Hi!
I'm appearing for DSAT on 11th March too. It's important to practice as many questions as possible, and not just watch videos. That includes completing the short tests.
Also, the practice tests on the Bluebook app are really helpful.
Good luck!
• How do I solve equations along the line of, "What is the value of tan(x degrees)"
• convert degress into radians, and then evaualte tan, or you can use sin/cos
(1 vote)
• I don't understand ! help
• What exactly dont you undertand?
(1 vote)
• Is that a general rule to remember, the side being opposite of 30* equals 1/2 of the radius? ()