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About Sherman D.
Expertise
I can answer questions dealing in mathematics of all kinds except for Physics and Calculus, but i can answer questions in Pre-Calculus and Chemistry. I can also answer questions in Recipes of all kinds. I can find games cheats/walkthroughs, but i can`t find a specific game online or offline. I can also do history and recipes for alcoholic beverages.

Experience
Mathematics, Recipes, History, and Games.

Education/Credentials
High School graduated. I graduated with honors, and i was in Beta Club for a year and a half.

Awards and Honors
Principle's list and A and B honor roll in high school only.

You are here: Experts > Science > Mathematics > Advanced Math > Proving Trig Identities

Topic: Advanced Math

Expert: Sherman D.
Date: 5/11/2008
Subject: Proving Trig Identities

Question
Hey I'm Molly i have trouble with proving identities, and
there was a question that i got confused about. It was

sin(x+y)
--------= tanx+tany
cosxcosy

Answer
sin(x + y)/(cos(x)cos(y)) = tan(x) + tan(y)

tan(x) + tan(y) =
(sin(x)/cos(x)) + (sin(y)/cos(y)) =
(sin(x)cos(y) + sin(y)cos(x))/(cos(x)cos(y)) =

this is the same as saying

sin(x + y)/(cos(x)cos(y)) =

or you could have done it this way

(sin(x)cos(y) + sin(y)cos(x))/(cos(x)cos(y)) =
((sin(x)cos(y))/(cos(x)cos(y))) + ((sin(y)cos(x))/(cos(x)cos(y))) =
(sin(x)/cos(x)) + (sin(y)/cos(y)) =
tan(x) + tan(y)

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