Question 522871
solve sin(5x)cos(8x)-cos(5x)sin(8x)=-0.5 for the smallest positive solution. 
x=
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Identity: sin(s-t)=sin s cos t-cos s sin t
sin(5x)cos(8x)-cos(5x)sin(8x)=-0.5
sin(5x-8x)=-0.5
sin(3x)=-0.5
3x=210º
x=70º