問MATHS 2000 C E MC Q.53 and Q.54－航空百大

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問MATHS 2000 C E MC Q.53 and Q.54

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問MATHS 2000 C E MC Q.53 and Q.54 可唔可以解釋下個答案點黎?

最佳解答:

MATHS 2000 C E MC Q.53 (C) Y=1-2cos2x When y = 0 ,for 0≦x≦π 1-2cos2x=0 Cos2x=1/2 2x=π/3,5π/3 ∴x=π/6,5π/6 When x=π/2, y=1-2cos2(π/2) =3 Area of the shaded region=1/2(3)(5π/6-π/6) =π MATHS 2000 C E MC Q.53 (D) Area of △ABC= 1/2(AB)(FG) = 4+5 =9 FG=18/AB Area of △ABE= 1/2(AB)(FE) = 4 FE=8/AB ∴FG:FE=18:8=9:4 FE+EG:FE=9:4 EG:FE=5:4 ∠ABE=∠CDE; ∠BAE=∠DCE (alt. ∠s,AB//DC) Also ∠AEB=∠CED (vert.opp.∠s) ∴△ABE～△CDE (AAA) ∴area of△CDE/area of△ABE=(EG/FE)^2=(5/4)^2=25/16 Area of △CDE=4(25/16)= 6.25cm2

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