Tuesday, 29 December 2015

trigonometry - Solving sin7phi+cos3phi=0




The question is find the general solution of this equation:sin(7ϕ)+cos(3ϕ)=0



I tried to use the "Sum-to-Product" formula, but found it only suitable for sin(a)±sin(b) or cos(a)±cos(b). So I tried to expand sin7ϕ and cos3ϕ, but the equation became much more complicated..



I'm self studying BUT There's nothing about how to solve this type of equations on my textbook..



reeeaaaaally confused now..


Answer



Hint: Use sum to product!
sin7ϕ+sin(π23ϕ)=0



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