What is the value of \(\displaystyle{{\sin{{47}}}^{\circ}+}{{\sin{{61}}}^{\circ}-}{{\sin{{25}}}^{\circ}-}{{\sin{{11}}}^{\circ}}\)

Teagan Horton

Teagan Horton

Answered question

2022-03-12

What is the value of sin47+sin61sin25sin11

Answer & Explanation

diesel817637dsf

diesel817637dsf

Beginner2022-03-13Added 13 answers

First we rearrange
X=sin47+sin61sin25sin11=sin47sin25+sin61sin11
In general, we have sinasinb=2cos(a+b2)sin(ab2) and therefore,
sin47sin25=2cos36sin11, and sin61sin11=2cos36sin25. Substituting to above, we obtain
X=2cos36(sin11+sin25)
We now have in general sina+sinb=2cos(ab2)sin(a+b2), and thus
X=4cos36sin18cos7
On the order hand, cos36=1+54 and sin18=514, and therefore, in fact
X=cos7

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