2006-06-15 02:46:05 · 5 answers · asked by Anonymous in Science & Mathematics ➔ Mathematics
cos175
= cos(180 - 5)
= -cos5
Now, cos15
= cos(45 - 30)
= cos45*cos30 + sin45*sin30
= {1/sqrt(2)}*{sqrt(3)/2} + {1/sqrt(2)}(1/2)
Thus cos15 can be calculated.
Now, cos(3*5) = 4*(cos5)^3 - 3*cos5
or cos15 = 4*(cos5)^3 - 3*cos5
Solve this cubic in (cos5) to get its value.
Hence you get cos175.
2006-06-15 03:26:56 · answer #1 · answered by psbhowmick 6 · 3⤊ 0⤋
Very good, but you need to go a little further. You want to use the "easy calculation" angles as much as possible. So you have cos 175º = cos (90º + 85º). cos 90º = 0, so that term drops out AND sin 90º = 1. Now cos 175º = -sin 85º. Look it up in a table.
2006-06-15 03:13:49 · answer #2 · answered by bequalming 5 · 0⤊ 0⤋
cos175=cos(180-5)
cos175= -cos5
2006-06-15 03:41:38 · answer #3 · answered by gari 3 · 0⤊ 0⤋
?=?cos[11? ? 12?] ?=?cos[(8? ? 12) + (3? ? 12)?] ?=?cos[(2? ? 3) + (? ? 4)?] ???... use the id:?cos(A+B)? =? (cosA??•??cosB)? ?? (sinA??•??sinB) ?=?cos(2? ? 3)??•??cos(? ? 4)? ?? sin(2? ? 3)??•??sin(? ? 4) ?=?(-?½)??•??(a million ? ??2)? ?? [(?3) ? 2?]??•??(a million ? ??2) ?=?-?(a million + ??3) ? (2??2)
2016-11-14 19:37:17 · answer #4 · answered by durgin 4 · 0⤊ 0⤋
cos(A+B)=cos(A)cos(B)-sin(A)sin(B)
Chek this site out
http://www.acts.tinet.ie/compoundanglesandcalcu_668.html
2006-06-15 02:57:29 · answer #5 · answered by Edward 7 · 0⤊ 0⤋