Page 93 - Math Grade 11 (Basic)

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2fntntnn 1 tLli]mtiJtint2J113 cos(60°- 30°)

Sb cos60°- cos30° <J &J:'l(f!S

cos - 30°) = cos30° = f = 0.866 sb

cos60°- cos30° = ~-f = ~( l /3) = -0.366 <J

nbfil~J:'lrul8l cos(60° 45°) = cos 15°
"' 1
tJ:'l~Sffimn cosl5° (f!Stf:Jlt1JinliH8lg~g timg !5° ~sr13sdl~~tftHu <J tJtHSg tJ:'l
c; 1 u

tJ:'l ~ s fiJ~ ~ci ~ m Ml:flUl ttl rnl:fls
t
·--7 --7 --7 ~ "" --7 _,.
(OA, OM)= a , (OA, ON)=~ Sb (OM, ON)= 0-a <J
-71COSO. -71 cos~
tt10l2 OM . ON '1
sma sin~

fil13S ru13s rud illJ:'lrul Mtru tJ:'lffitHdHnH:
t n
...:. -7
OM· ON= OM· ON· cos(~-a) = cos(~-a) tLmg

cos(a- ~) = cos a cos~+ sin a sill;] ( l) '1

cosl5° = cos(60° -45°) = cos60°cos45° + sin60°sin45°

= !xJ2+J3xJ2=J2+J6 '1
2 2 2 2 4

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