∑16r=1√1+cos4r=
4√2 sin1∘ cos2∘ cos17∘
4√2 cos1∘ cos2∘ cos17∘
4√2 cos1∘ sin2∘ cos17∘
None of these
∑16r=1√1+cos4r=∑16r=1√2cos2r
=√2(cos2∘+cos4∘+cos6∘+⋯⋯+cos32∘)
=√2sin16∘sin1∘cos{2+(15)(1)}=√2sin16∘cos17∘sin1∘