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数学
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如图,梯形ABCD中,AD∥BC,DC⊥BC,将梯形沿对角线BD折叠,点A恰好落在DC边上的点A′处,若∠A′BC=20°,则∠A′BD的度数为( )
A. 15°
B. 20°
C. 25°
D. 30°
人气:110 ℃ 时间:2020-05-24 15:36:57
解答
∵∠A′BC=20°
∴∠BA′C=70°
∴∠DA′B=110°
∴∠DAB=110°
∴∠ABC=70°
∴∠ABA′=∠ABC-∠A′BC=70°-20°=50°
∴∠A′BD=
1
2
∠ABA′=25°.
故选C.
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