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電子課本網(wǎng) 第29頁(yè)

第29頁(yè)

信息發(fā)布者:
解:?$15×\frac {\sqrt 5-1}2≈9.27\ \mathrm {m}$?
∴應(yīng)該站在離?$A$?點(diǎn)?$9.27\ \mathrm {m}$?處,或距?$B$?點(diǎn)?$9.27\ \mathrm {m}$?處
解:?$(1)$?∵點(diǎn)?$P$?是線段?$AB$?的黃金分割點(diǎn),?$AP<BP$?
∴?$BP=\frac {\sqrt {5}-1}2×AB=\frac {\sqrt 5-1}2=\sqrt 5-1$?
∴?$AP=AB-BP=2-(\sqrt {5}-1)=3-\sqrt {5}$?
?$(2)$?∵?$QP{平分}∠AQB$?
∴?$P$?到?$AQ、$??$BQ$?的距離相等
∴?$\frac {S_{△PAQ}}{S_{△PBQ}}=\frac {AQ}{BQ}=\frac {AP}{PB}$?
又由?$(1)AP=BQ=3-\sqrt {5}$?
∵?$AB=2$?
∴?$PB=AB-AP=2-(3-\sqrt {5})=\sqrt {5}-1$?
∴?$AQ=\frac {AP·BQ}{PB}=\frac {(3-\sqrt 5)^2}{\sqrt 5-1}=2\sqrt {5}-4$?
解:?$(1)$?由題意可得?$ \frac {AB}{AF}=\frac {\sqrt{5}-1}{2}$?
又∵?$AF=1$?
∴?$AB=\frac {\sqrt{5}-1}{2} $?
?$(2)$?矩形?$DCGF $?是黃金矩形
∵四邊形?$ABCD$?是正方形
∴?$AB=DC=AD$?
又∵?$\frac {AB}{AF}=\frac {\sqrt{5}-1}{2}$?
∴?$\frac {AD}{AF}=\frac {\sqrt{5}-1}{2},$?即?$D$?是線段?$AF $?的黃金分割點(diǎn)
∴?$\frac {FD}{AD}=\frac {\sqrt{5}-1}{2}$?
∴?$\frac {FD}{CD}=\frac {\sqrt{5}-1}{2}$?
∴矩形?$DCGF $?是黃金矩形 
?$(3)$?若圖③中最大黃金矩形的長(zhǎng)為?$a,$?
由題意可得,最小黃金矩形的長(zhǎng)是?$(\frac {\sqrt{5}-1}{2})^6a$?