testing header
Math Goodies is a free math help portal for students, teachers, and parents.
Free Math
Newsletter
 
 
Interactive Math Goodies Software

Buy Math Goodies Software
testing left nav
Math Forums @ Math Goodies
Math Forums @ Math Goodies
Home | Profile | Register | Active Topics | Members | Search | FAQ
 All Forums
 Homework Help Forums
 Geometry and Trigonometry
 using the cosine sum and difference to find values

Note: You must be registered in order to post a reply.
To register, click here. Registration is FREE!

Screensize:
UserName:
Password:
Format Mode:
Format: BoldItalicizedUnderlineStrikethrough Align LeftCenteredAlign Right Horizontal Rule Insert HyperlinkInsert EmailInsert Image Insert CodeInsert QuoteInsert List Insert Special Characters Insert Smilie
   
Message:
* HTML is OFF
* Forum Code is ON

Math Symbols
Squared [squared] Cubed [cubed] Square Root [sqrt] Cube Root [cbrt] Pi [pi]
Alpha [alpha] Beta [beta] Gamma [gamma] Theta [theta] Angle [angle]
Degrees [degrees] Times [times] Divide [divide] Less Than or Equal To [less-than] Greater Than or Equal To [greater-than]
Plus Minus [plus-minus] Integral [integral] Sum [sum] Sub 1 [sub-1] Sub 2 [sub-2]
Element Of [element-of] Union [union] Intersect [intersect] Subset [subset] Empty Set [empty-set]

  Check here to subscribe to this topic.
 
   

T O P I C    R E V I E W
Cortez Mos Posted - 10/17/2007 : 23:16:16
cos(-10)cos 35+ sin(-10) sin 35
4   L A T E S T    R E P L I E S    (Newest First)
sahsjing Posted - 10/18/2007 : 17:37:35
Another approach:
cos(-10)cos 35+ sin(-10) sin 35
= sin80 cos35 - cos 80 sin35
= sin(80-35)
= sin 45
= 2 / 2
the_hill1962 Posted - 10/18/2007 : 07:34:54
I believe the formula that royhaas is referring to is:
cos(A−B) = cos A cos B + sin A sin B
At least that is the obvious one to me from the following that you should have seen before being assigned this problem:
1. cos(A+B) = cos A cos B − sin A sin B
2. sin(A+B) = sin A cos B + cos A sin B
3. cos(A−B) = cos A cos B + sin A sin B
4. sin(A−B) = sin A cos B − cos A sin B
The reason that we pick out the 3rd one is because your problem is
cos(-10)cos 35+ sin(-10) sin 35
Notice if you have A=-10 and B=35
then your problem is
cos(A)cos(B) + sin(A)sin(B) which is EXACTLY what the 3rd identity states that cos(A-B) is equal to.
Now all you have to do is the simple problem of subtracting B from A (which in your case is -35 minus 10.
-35-10=-45
So, since you problem is equivalent to cos(A-B) where A=-10 and B=35,
it is cos(-10 - 35), and that is cos(-45).
Now, you should already know that cos(-45) is equal to (2)/2
Cortez Mos Posted - 10/17/2007 : 23:25:35
example please
royhaas Posted - 10/17/2007 : 23:24:30
Just plug into the formula and simplify.

Math Forums @ Math Goodies © 2000-2004 Snitz Communications Go To Top Of Page
This page was generated in 0.09 seconds. Snitz Forums 2000
testing footer
About Us | Contact Us | Advertise with Us | Facebook | Blog | Recommend This Page




Copyright © 1998-2014 Mrs. Glosser's Math Goodies. All Rights Reserved.

A Hotchalk/Glam Partner Site - Last Modified 01 Oct 2014