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F.4數學功課 (20分!)(3)

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14. ABCD is a parallelogram in which AC=7cm and BD =10cm.The diagonals AC and BD intersect at K and Angle BKC =74°.Find its area.15.(a) Let a/20 = b/21 = c/29 =k.Express a,b,c in terms of k.(b) Find the greatest angle of a triangle in which its lengths are in ratio 20:21:29.16. The period of the... 顯示更多 14. ABCD is a parallelogram in which AC=7cm and BD =10cm.The diagonals AC and BD intersect at K and Angle BKC =74°.Find its area. 15. (a) Let a/20 = b/21 = c/29 =k.Express a,b,c in terms of k. (b) Find the greatest angle of a triangle in which its lengths are in ratio 20:21:29. 16. The period of the function f(x)=cos(2x-45°) is...? 17. In Traingle ABC,a:b:c=2:5:6.Find cosA:cosB:cosC.

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14. ABCD is a parallelogram in which AC=7cmand BD =10cm.The diagonals AC and BD intersect at K and Angle BKC =74°.Find its area. Sol Area=7*10*sin74°=67.288 15. (a) Let a/20 = b/21 = c/29 =k.Express a，b，c in terms ofk. Sol a=20k，b=21k，c=29k (b) Find the greatest angle of a triangle in which its lengths are in ratio 20：21：29. Sol 設最大角角度=w Cosw=(20^2+21^2－29^2)/(2*20*21)=0 w=90°. 16. The period of the function f(x)=Cos(2x－45°) is...? Sol 360°./2=180°. 17. In Traingle ABC，a：b：c=2：5：6.Find CosA：CosB：CosC. Sol CosA=(25+36－4)/(2*5*6)=57/60 CosB=(4+36－25)/(2*4*6)=15/48 CosC=(4+25－36)/(2*4*5)=-7/40 CosA：CosB：CosC =57/60：15/48：－7/40 =456：150：－84 =76：25：－14

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