ATAR Notes: Forum

VCE Stuff => VCE Mathematics => VCE Mathematics/Science/Technology => VCE Subjects + Help => VCE Specialist Mathematics => Topic started by: Sumboody on March 15, 2011, 08:10:42 pm

Title: Trig Help !
Post by: Sumboody on March 15, 2011, 08:10:42 pm: cos(x)=0.6 and is in the 4th quadrant, how do i find sin(x/2) ?
Title: Re: Trig Help !
Post by: DannyN on March 15, 2011, 08:54:05 pm: you can inverse cos(x)=0.6 to get an angle, your calculator would probably give you an angle in the first quadrant
i got x=53.13 degrees ,so it would be -53.13 degrees in the forth quadrant

then sub x=-53.13 into sin(x/2)=sin(-53.13/2) which gives you -.447
Title: Re: Trig Help !
Post by: Sumboody on March 15, 2011, 08:59:23 pm: Thanks :)
but is it possible without a calculator?
Title: Re: Trig Help !
Post by: kamil9876 on March 15, 2011, 09:27:43 pm: Use:

$cos(2\theta)=1-2sin^2(\theta)$

If you want.
Title: Re: Trig Help !
Post by: pi on March 15, 2011, 09:29:57 pm: Draw a triangle and use pythag, and then create the half angle formula with
Quote from: kamil9876 on March 15, 2011, 09:27:43 pm
Use:

$cos(2\theta)=1-2sin^2(\theta)$

If you want.