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CBSE Class 10 Answered

find the value of cos15. cos16. cos17. ....................cos74. cos75
Asked by saransh.gupta27 | 18 Jan, 2019, 01:08: AM
answered-by-expert Expert Answer
let F = cos15 cos16 cos17......................cos74 cos75
 
F = [ cos15 cos75 ] [ cos16 cos74 ] [ cos17 cos73]....... [cos43 cos47] [cos44 cos46] cos45
 
F = (30/2) [cos90+cos60][cos90+cos58][cos90+cos56]..............[cos90+cos2] cos45
 
F = 15 cos60 cos58 cos56.............cos4 cos2 cos45
 
F = 15 [cos60cos30] [cos58 cos32][cos56 cos34][cos54 cos36][cos52 cos38][cos50 cos40][cos48 cos42][cos46 cos44]cos28 cos26 .......cos4cos2cos45
 
F = 15×8×(1/2)[cos90+cos30][cos90+cos26].......................................................[cos90+cos6][cos90+cos2]cos28 cos26.......cos4 cos2 cos45
 
F = 60 cos30 cos26 cos22 cos18 cos14 cos10 cos6 cos2 cos28 cos26 cos24 cos22 cos20 cos18 cos16 cos14 cos12 cos10 cos8 cos6 cos4 cos2 cos45
 
F = 60×(1/2)×(1/√2) cos28 cos226 cos24 cos222 cos20 cos218 cos16 cos214 cos12 cos210 cos8 cos26 cos4 cos22
Answered by Thiyagarajan K | 20 Jan, 2019, 18:16: PM

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