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Question : 21 of 160
Marks:
+1,
-0
Solution:
sin25°+sin210°+sin215°+...+sin290° ⇒sin25°+sin210°+...+sin245°+sin250° +...+sin280°+sin285°+sin290° ⇒{sin(90−85°)}2+{sin(90−80)}2+... +{sin(90−50)}2+sin245°+sin250°+... +sin280°+sin289°+sin290° ⇒cos285°+cos280°+... +cos250°+sin245°+sin250° +...+sin280°+sin285°+sin290° ⇒(sin285°+cos285°) +(sin280°+cos280°) +...+(sin250°+cos250°)+sin245°+sin290° ⇒1+1+...1++1=9
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