This afternoon I've been studying the pythagorean identities & compound angles. I've got a problem with a question working with 2 sets of compound angles:
Solve, in the interval 0∘≤θ≤360∘, cos(θ+25∘)+sin(θ+65∘)=1
I've attempted expanding but reach a point with no common factors & see how to manipulate the trig ratios to move on; is there a solution without expanding?
cosθcos25∘−sinθsin25∘+sinθcos65∘+sin65∘cosθ=1
cosθ(cos25∘+sin65∘)+sinθ(cos65∘−sin25∘)=1
Could you tell me if I've made a mistake or how I could continue;
thanks
coffee is wearing out
Answer
"Solve, in the interval 0≤θ≤360, cos(θ+25)+sin(θ+65)=1"
cos(θ+25)+cos(25−θ)=1
∵ sin(θ+65)=cos(90−(θ+65))=cos(25−θ)
cos(θ)cos(25)−sin(θ)sin(25)+cos(25)cos(θ)+sin(θ)sin(25)=1
2cos(θ)cos(25)=1
cos(θ)=12cos(25)
∴θ≈55.6°,326.5°
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