Monday

October 20, 2014

October 20, 2014

Posted by **Writeacher** on Monday, February 9, 2009 at 7:01am.

i don't understand the sine and cosine rules.

1/2 ab sinC

and cosA= b2 + c2 - a2

what???

i have asked my teacher but i still don't get it.

- Math repost - girly93 -
**bobpursley**, Monday, February 9, 2009 at 9:50amYour question makes no sense to me.

The law of cosines is this

a^2=b^2+c^2 - 2bc * CosA

I have no idea what 1/2 ab SinC is , unless it is the area formula for a triangle. You need to be more specific.

- Math repost - girly93 -
**drwls**, Monday, February 9, 2009 at 9:50amThe law of cosines, in one form, is

a^2 = b^2 + c^2 - 2bc cos A

The law of sines is

a/sin A = b/sinB = c/sinC

= 2R

Your cosA equation is incorrect.

(1/2) a b sin C is a formula for the area of a triangle, and has nothing to do with the law of sines.

For more about these equations, see

http://www.mathcentre.ac.uk/resources/workbooks/mathcentre/web-sinecostri.pdf

**Answer this Question**

**Related Questions**

TRIG! - Posted by hayden on Monday, February 23, 2009 at 4:05pm. sin^6 x + cos^6...

Geometry - The word cosine literally means "the complement of the sine." Write a...

Algebra2--- - 1. An artist is designing triangular mirrors. Determine the number...

Algebra 2 .. - 1. An artist is designing triangular mirrors. Determine the ...

Algebra 2.... - 1. An artist is designing triangular mirrors. Determine the ...

MATH - Posted by xavier on Monday, February 11, 2013 at 8:28pm. Hello... Asking ...

MATH PLEASE HELP SUE - # Math - bobpursley, Monday, September 14, 2009 at 5:24pm...

sine and cosine - Simplify and write the trigonometric expression in terms of ...

cosine and sine HELP! - Simplify and write the trigonometric expression in terms...

Graphing trigonometric function - sine and cosine have a period 2pi tangent and ...