Posted by jeff on Sunday, May 16, 2010 at 9:14am.
You should become familiar with two important special triangles
1. the 45-45-90 right-angled triangle whose sides are in the ratio
1 : 1 : √2
2. the 30-60-90 right-angled triangle whose sides are in the ratio of
1 : √3 : 2
The question to find sin 315° probably says to find it "exactly"
I do these in a 3-step process
1. Where is the angle?
315 is in IV and in IV the sine is negative
2. How far from the x-axis ?
315° is 45° from the x-axis
The answer to this question will always be an angle between 0 and 90, it will be called the "angle in standard position, or ASP)
3. Rewrite the question in terms of the ASP
sin 315 = -sin 45
From your special triangles
sin 45 = 1/√2 or √2/2 after rationalizing
so sin 315 = -sin 45 = -√2/2
In the matrix below, which element is a1,2?
1
4
7
2
5
8
3
6
9
A. 8 C. 6
B. 5 D. 2
Examination
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