Trigonometry: Using Sum and Difference Formulas
 This is a free lesson from our course in Trigonometry In this lesson you'll learn more details of how to find the values of the sine and the cosine functions using the sum and difference formulas. It is explained by instructor with the help of a video having some examples and practice questions with solution. It is used in trigonometric applications to find the values of sine and cosine functions for which the angle measures are given in degree or in radians and also to evaluate expressions for which the angle measures of A and B are unknown. (More text below video...)
Other useful lessons:
 Sum and Difference Formulas Double and Half Angle Formulas Using Double and Half Angle Formulas
(Continued from above) For example: Let us find value of sin (A + B); where sin A = 3/5, cos B = 9/41 and 0 < A, B< /2.  You can use Pythagorean Theorem x2 + y2 = r2 and sin  A = 3/5 i.e. y/r, to get cos A = 4/5.
Similarly, using the Pythagorean Theorem and cos B = 9/41 i.e. x/r, you'll get sin B = 40/41. Now substitute these values in sin (A + B) = sin A cos B + cos A sin B. You will get the answer 187/205.
Winpossible's online math courses and tutorials have gained rapidly popularity since their launch in 2008. Over 100,000 students have benefited from Winpossible's courses... these courses in conjunction with free unlimited homework help serve as a very effective math-tutor for our students.
 - All of the Winpossible math tutorials have been designed by top-notch instructors and offer a comprehensive and rigorous math review of that topic. - We guarantee that any student who studies with Winpossible, will get a firm grasp of the associated problem-solving techniques. Each course has our instructors providing step-by-step solutions to a wide variety of problems, completely demystifying the problem-solving process! - Winpossible courses have been used by students for help with homework and by homeschoolers. - Several teachers use Winpossible courses at schools as a supplement for in-class instruction. They also use our course structure to develop course worksheets.

 Copyright © Winpossible, 2010 - 2011 Best viewed in 1024x768 & IE 5.0 or later version