Posted by **sophie** 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 -
**bobpursley**, 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 -
**sophie**, Monday, June 1, 2009 at 8:53pm
it's B?

- Math -
**Reiny**, 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 -
**sophie**, Monday, June 1, 2009 at 9:11pm
no those are the options for sure :/

- Math -
**MathMate**, 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 sin2**5**5

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