cos8π7cos10π7cos12π7=cos8π7cos(2π−4π7)cos(2π−2π7)=cos8π7cos4π7cos2π7=2sin2π7cos2π7cos4π7cos8π72sin2π7=2sin4π7cos4π7cos8π74sin2π7=2sin8π7cos8π78sin2π7=sin16π78sin2π7=sin(2π+2π7)8sin2π7=−sin2π78sin2π7=−18
1(√9−√8)−1(√8−√7)+1(√7−√6)−1(√6−√5)+1(√5−√4) is equal to:
14×(1+12)×(1+34)×(1+54)×(1+74) is equal to: