We need to prove that 16sin(24π)sin(245π)sin(247π)sin(2411π)=1. First, we can rewrite sin(2411π) as sin(π−2413π)=sin(2413π). Also, sin(2413π)=sin(2π+24π)=cos(24π). So, the expression becomes:
16sin(24π)sin(245π)sin(247π)cos(24π) =16sin(24π)cos(24π)sin(245π)sin(247π) =8(2sin(24π)cos(24π))sin(245π)sin(247π) We use the formula 2sinxcosx=sin2x. Then: 8sin(242π)sin(245π)sin(247π) =8sin(12π)sin(245π)sin(247π) sin(12π)=sin(15∘)=sin(45∘−30∘)=sin45∘cos30∘−cos45∘sin30∘=2223−2221=46−2 Also, sin(245π)=sin(37.5∘) and sin(247π)=sin(52.5∘). Using the product-to-sum formula, we have:
sinasinb=21[cos(a−b)−cos(a+b)] sin(245π)sin(247π)=21[cos(242π)−cos(2412π)]=21[cos(12π)−cos(2π)]=21cos(12π) Since cos(12π)=cos(15∘)=46+2, we have sin(245π)sin(247π)=21(46+2)=86+2 Therefore,
8sin(12π)sin(245π)sin(247π)=8(46−2)(86+2)=8(326−2)=8(324)=8(81)=1