Maths

(1) Width of metal sheet is between 7.5 and 8.5 cm.
Length of metal sheet is between 9.5 and 10.5 cm.
So smallest area = 7.5 x 9.5 = 71.25 cm2.
Largest area = 8.5 x 10.5 = 89.25 cm2.
so range is 71.25 < = x < 89.25. Ans. is (A).
(2)
Since the chords are equal, the perpendicular distance from the center of the circle to the 3 chords are equal. So O is the center of the inscribed circle with the 3 chords as tangents. Thus OR and OQ are angle bisectors of angle PRD and angle PQC respectively.
Let angle PRO = x and let angle PQO = y.
From triangle ORQ, angle QOR + x + y = 180 ...........(1)
Also, angle RPQ + angle PEO + angle PQO = angle QOR
that is 38 + x + y = angle QOR
x + y = angle QOR - 38
Sub into (1)
angle QOR + ( angle QOR - 38) = 180
2 x angle QOR = 180 + 38 = 218
angle QOR = 218/2 = 109 degree. Ans is (A).
(3)
Angle ADC = 90 degree ( angle in semi - circle)
Angle ADC + angle ADE + angle CBE = 180 degree ( opposite angle of cyclic quad.)
90 + 28 + angle CBE = 180
angle CBE = 180 - 90 - 28 = 62. Ans. is (B)

由於時間關係，或者我幫 wy 解釋一下吧。

其實每一步，由於四捨五入的關係，等於符號都是在前方：

7.5 cm ≤ width < 8.5 cm

9.5 cm ≤ length < 10.5 cm

71.25 cm² ≤ area < 89.25 cm²

因此，是 (A)，不是 (B) 。

明白嗎？

2014-05-04 17:12:32 補充：
舉例，如果 width 真的達到 8.5 cm，那應該是量出 9 cm, 不是 8 cm。

如果量出 8 cm, with maximum absolute error (最大絕對誤差) = 0.5 cm

那麼就是 7.5 cm ≤ width < 8.5 cm

To wy

(1): 計算了最大面積與最小面積之後,用什麼方法去確定答案是A而不是B?