# Thread: Maths help

1. ## Maths help

give the exact value for sin(-225)
i am getting sq root 3 / 2 but answer is 1/sq root 2
Why

2. ## Re: Maths help

Originally Posted by highshill
give the exact value for sin(-225)
i am getting sq root 3 / 2 but answer is 1/sq root 2
Why
Note

sin(-225 deg) = -sin(225 deg) (sin is odd)

= -sin((180-225) deg) (recall the identity sin(180 deg – X) = sin X)

= -sin(-45 deg)

= sin(45 deg)

= 1/(sqrt(2)).

3. ## Re: Maths help

so when do i apply these identities

4. ## Re: Maths help

Originally Posted by highshill
so when do i apply these identities
You can use them to get the given angle down to a number that you known the exact trig. value of.

5. ## Re: Maths help

like my book does not use it, but the answers are a following that identity have i understood the concept wrong

6. ## Re: Maths help

Originally Posted by highshill
like my book does not use it, but the answers are a following that identity have i understood the concept wrong
Is it Maths In Focus?

yes

8. ## Re: Maths help

Originally Posted by integrand
is it maths in focus?
hhahahahha

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