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Expert: Alon Mandes - 9/10/2009


Question
prove that (sinA.sin2A+sin3A.sinA6A)/(sinA.cos2A+sin3A.cos6A)=5tanA

(sinA.sin2A+sin3A.sinA6A)/(sinA.cos2A+sin3A.cos6A)
=(2sinA.sin2A+2sin3A.sinA6A)/(sinA.cos2A+2sin3A.cos6A)
=(cos(2A-A)-cos(2A+A)+cos(6A+3A)-cos(6A+3A))/(sin(2A+A)-sin(2A-A)+sin(6A+3A)-sin(6A-3A))
=(cosA-cos3A+cos3A-cos9A)/(sin3A-sinA+sin9A-sin3A)
=(cosA-cos9A)/(sin9A-sinA)
=(2sin5A.sin4A)/(2cos5A.sin4A)=tan5A

sir please explain how this statement (sinA.sin2A+sin3A.sinA6A)/(sinA.cos2A+sin3A.cos6A)

became (2sinA.sin2A+2sin3A.sinA6A)/(sinA.cos2A+2sin3A.cos6A).please reply

Answer
This statement is not correct . It should be :
(sinA.sin2A+sin3A.sinA6A)/(sinA.cos2A+sin3A.cos6A)=
(2sinA.sin2A+2sin3A.sinA6A)/(2sinA.cos2A+2sin3A.cos6A).
Note that I have added multiplying of 2 in the half down fracture . Now its correct.
It's the same as to claim that : (a+b)/(c+d) = (2a+2b)/(2c+2d) .

Alon.  

Calculus

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Alon Mandes

Expertise

Kind of questions I can answer : Limits, Derivatives, Integration, Implicit functions, continuousity, differentiation ,Extremum problems, Lagrange multipliers, Gradients, Surface integrals, Multi variables functions ,Multi variables Integrals,Complex variables ,Complex functions, Curves, Trajectory integrals & Vector analyse,Divergence,Rotor & word problems. Kind of question I can't answer : Economics,Combinatorics,infinite series & convergence ,Statistics & Probabilities .

Experience

1. I'm a team member of mathnerds (math site for answering questions) 2. I'm a team member in the Student's Union of the Technion, helping students who have problems in mathematics. 3. 2 years of experience as a math teacher in college. 4. I give free homework help for high school students in Mathematics & Physics. 5. I teach part time in collage the subjects : "Digital Signal Processing" , "Random Signals & Noise" , "Complex Functions".

Organizations
Hi-Tech company : GSM4VOIP ; job possition : Algorythm developer.

Education/Credentials
M.A in Mathematics & Bs.c in Electronics.

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