SOLUTION: find the exact value of sin(1125° + 480°) using sum and difference formulas

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Question 797301: find the exact value of sin(1125° + 480°) using sum and difference formulas
Answer by lwsshak3(11628) About Me  (Show Source):
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find the exact value of sin(1125° + 480°) using sum and difference formulas
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1125=1125-3*360=1125-1080=45deg=reference angle of 45deg in quadrant I
480deg=480-360=120deg=reference angle of 60deg in quadrant II
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Identity:sin(a+b)=sin(a)cos(b)+cos(a)sin(b)
sin(a)=sin(1125)=sin(45)=√2/2
cos(b)=cos(480)=cos(120)=cos 60(in quadrant II)=-1/2
cos(a)=cos(1125)=cos(45)=√2/2
sin(b)=sin(480)=sin(120)=sin(60)(in quadrant II)=√3/2
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sin(a+b)=sin(a)cos(b)+cos(a)sin(b)
sin(a+b)=√2/2*(-1/2)+√2/2*√3/2
=-√2/4+√6/4
=(-√2+√6)/4
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Check:
sin(1125° + 480°)=sin(1605)=sin(165)≈0.2588..
Exact value as calculated=(-√2+√6)/4≈0.2588..