5/17 Geometry Bell Ringer A circle has an area of 64π sq. in.

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Presentation transcript:

5/17 Geometry Bell Ringer A circle has an area of 64π sq. in. What is the circumference? Draw a picture of this circle with the radius labeled. Homework: DUE FRIDAY: p. 451 (#1 – 8, 11 – 14) p. 455 (#1, 3, 6, 7, 9, 11)

5/17 News and Notes Perfection: 8th Period Missing Quizzes: 1st: Tracia, LaFontae, Brandey 7th: Good. 8th: Desirae, Arely, Diego Tutoring TOMORROW

Take 3 minutes and try to solve on your own or with person next to you Find the distance from A to B by going around the circle. A B

So what’d you do? Found the circumference of the whole circle. Divided by two (or multiplied by 0.5)

What’d you just find? You found the length of an arc. Arc – A part of the distance around a circle. In this case, your arc was half of the circle. B

Example #1 Step 1: Find circumference of circle C = 2πr C = 2π * 18 C = 36π cm Step 2: Find measurement of arc’s angle Step 3: m Arc / 360 Step 4: Multiply together

Step 2: Find measurement of arc’s angle 360 – 150 = 210° Step 2b: m Arc / 360  How much of the circle? 210/360 Step 3: Multiply together

To Review To find an arc length, you must know 3 things: 1. Circumference 2. How much out of 360° is the arc? 3. Multiply together

Guided Practice – Beat the clock! Find length of CD #1 – Find C C = 2πr C = 2π(10) C = 20π inches #2 – Find arc fraction 90/360 = 0.25 #3 – Find arc length D r = 10 in. A

Independent Practice Remember that the RADIUS is the key that unlocks everything!!!!

Exit Ticket 1. Find the length of AB 2. What did you learn about today? Be as precise as possible.