AMC 8 1988 Problem 5

AMC8 1988 年第 5 题

四边形与多边形★☆☆☆☆

Problem If

\angle CBD

is a right angle, then this protractor indicates that the measure of

\angle ABC

is approximately

如果

\angle CBD

是直角，则该量角器显示

\angle ABC

的近似度数是

A. $20^\circ$
B. $40^\circ$
C. $50^\circ$
D. $70^\circ$
E. $120^\circ$

正确答案 · Correct Answer

C

解析 · Solution

Solution 1

\angle OBA = 20^{\circ}

,

\angle CBD = 90^{\circ}

, and

\angle OBD = 160^{\circ}

. So

\angle ABC = 160^{\circ} - 20^{\circ} - 90^{\circ} = 50^{\circ}

.

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