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Posted by on Monday, June 1, 2009 at 8:26pm.

Use a sum or difference identity to find the exact value of sin225°
a. (-√2 - √6)/4
b. (√6 - √2)/4
c. (√6 + √2)/4
d. (√2 - √6)/4

is it A?

  • Math - , Monday, June 1, 2009 at 8:47pm

    a) is the sine of 285
    b) is the sine of 15, 165
    c) is the sine of 75, 105
    d) is the sine of -15, 195

    check my thinking.

  • Math - , Monday, June 1, 2009 at 8:53pm

    it's B?

  • Math - , Monday, June 1, 2009 at 8:54pm

    none of the given answers is correct.
    Are you sure you typed it correctly?

    sin 225 = sin(180+45)
    = sin180cos45 + cos180sin45
    = 0 + (-1)√2/2
    = -√2/2

  • Math - , Monday, June 1, 2009 at 9:11pm

    no those are the options for sure :/

  • Math - , Monday, June 1, 2009 at 11:22pm

    Are you sure it is not
    > Use a sum or difference identity to find the exact value of sin255

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