ATAR Notes: Forum

VCE Stuff => VCE Mathematics/Science/Technology => VCE Subjects + Help => VCE Mathematics => Topic started by: geminii on July 19, 2014, 01:42:41 pm

Title: Maths homework help? (Sin, cos, tan)
Post by: geminii on July 19, 2014, 01:42:41 pm

Hi guys, I'm having trouble with this maths problem (16.a) and I don't know where I'm going wrong. My answer was 21.1 degrees, but the answers say that it is 68.9 degrees. Please help and tell me where I've gone wrong!! :(
Thanks heaps!!  :)

Title: Re: Maths homework help? (Sin, cos, tan)
Post by: geminii on July 19, 2014, 01:48:28 pm

I used sin:

Using sin,
Sin(thita) = 1.8/5
(thita) = sin(inverse) x 1.8/5
I put this into the calculator and it came up with 21.10019602.

I don't know what happened?

Title: Re: Maths homework help? (Sin, cos, tan)
Post by: pi on July 19, 2014, 01:48:45 pm

theta = cos^-1 (adjacent/hypotenuse) = cos^-1 (1.8/5) = 68.9 degrees

You use cosine as they've given you the adjacent side to the angle, not the opposite side which would make sine a logical choice.

Title: Re: Maths homework help? (Sin, cos, tan)
Post by: geminii on July 19, 2014, 01:57:48 pm

I don't get why you use cosine? Because the 1.8 is the opposite (of the angle) and the 5 is the hypotenuse so wouldn't you use sin?
Thanks :)

Title: Re: Maths homework help? (Sin, cos, tan)
Post by: pi on July 19, 2014, 02:07:20 pm

Ah I didn't read the question correctly, you're completely right :)

Title: Re: Maths homework help? (Sin, cos, tan)
Post by: geminii on July 19, 2014, 02:09:38 pm

Ahh thanks
Haha sometimes they get the answers wrong in the book :)
Thanks!   ;D