Trigonometry Sum and Difference Identities

by Michael Stueben from

Twenty Years Before the Blackboard Edited by Mrs. Larimore

http://www.doe.virginia.gov/Div/Winchester/jhhs/math/lessons/trig/sumdif.html

April 29, 2009

Sinbad and Cosette

A Love Story?

Sinbad loved Cosette ….

…but Cosette did not feel the same way about Sinbad.

Sinbad and Cosette’s parents were friends and the two had to go out on dates

In order for it not to be too painful, they brought their siblings

Naturally, when Sinbad was in charge of their double date, he put himself with Cosette, and he put his brother with her sister:

Sinbad loved to tell people that his and Cosette's signs were the same.

• sin(A + B) = sin A cosB + cosA sinB. • sin(A - B) = sin A cosB - cosA sinB.

However, when Cosette was in charge of the double date she placed herself with her sister and put Sinbad with his brother

She made sure everyone knew that their signs were NOT the same:

• cos(A + B) = cosA cosB - sinA sinB. cos(A - B) = cosA cosB + sinA sinB. • Also, notice that Cosette placed herself and her sister BEFORE Sinbad and his brother. This detail was important to Cosette. She was very snobby, you know.

And that is the story of Sinbad and Cosette…… THE END Feedback: Was this a useful tool for remembering the formulas?

Bonus: If positive feedback….. 1) You can make a photo-story of the story and narrate it 2) You can make a children’s book and illustrate it