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tanA=a/b=9/6,用计算器计算,得∠A≈56.3°.
∴∠B≈90°-56.3°=33.7°.
(2)由题意知,sinA=a/c,
则a=c.sinA=13×sin 18°≈4.0.
cos A=b/c,则b=c.cos A=13×cos 18°≈12.4.
∠B=90°-∠A=90°-18°=72.0°.
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