Angles and the CCSS – oops!

Check this out:

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Grade 4 content
Geometric measurement: understand concepts of angle and measure angles.
5. Recognize angles as geometric shapes that are formed wherever two rays share a common endpoint, and understand concepts of angle measurement:
a. An angle is measured with reference to a circle with its center at the common endpoint of the rays, by considering the fraction of the circular arc between the points where the two rays intersect the circle. An angle that turns through 1/360 of a circle is called a “one-degree angle,” and can be used to measure angles.
b. An angle that turns through n one-degree angles is said to have an angle measure of n degrees.

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My comments:
1. Well, this is the first occasion that the word “ray” is used, in the whole document, and as expected by now there is no definition!
2. There is an attempt to define measurement of angle, which really confuses me.  Which circle ? Any circle ? What is “the circular arc” ? Since when did angles turn ? And I have this vision of making a one degree angle out of card and measuring angles with it.
3. An this is from the Fractions section : “note 3 Grade 4 expectations in this domain are limited to fractions with denominators 2, 3, 4, 5, 6, 8, 10, 12, and 100.”
So what about 1/360 ?

Am I nitpicking again?

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Filed under fractions, geometry, language in math

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