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第二十六章　解直角三角形
26. 2 锐角三角函数的计算
INCLUDEPICTURE"复习回顾.tif" INCLUDEPICTURE "D:\\课件\\九数JJ河北（北京）\\复习回顾.tif" \* MERGEFORMATINET INCLUDEPICTURE "D:\\课件\\九数JJ河北（北京）\\复习回顾.tif" \* MERGEFORMATINET
1．用计算器求－53，按键的顺序正确的是(　　)
2．用四舍五入法对0.060 45取近似值，错误的是(　　)
A．0.1(精确到0.1) B．0.06(精确到百分位)
C．0.061(精确到千分位) D．0.060 5(精确到0.000 1)
3．在下面的表中，填出 30°，45°，60°角的正弦值、余弦值和正切值．
30° 45° 60°
sin α
cos α
tan α
INCLUDEPICTURE"预习效果检测.tif" INCLUDEPICTURE "D:\\课件\\九数JJ河北（北京）\\预习效果检测.tif" \* MERGEFORMATINET INCLUDEPICTURE "D:\\课件\\九数JJ河北（北京）\\预习效果检测.tif" \* MERGEFORMATINET
1．用计算器计算sin 24°的值，以下按键顺序正确的是(　　)
A. B.
C. D.
2．如图，一座厂房屋顶人字架的跨度AC＝12 m，上弦AB＝BC，∠BAC＝25°.若用科学计算器求上弦AB的长，则下列按键顺序正确的是(　　)
INCLUDEPICTURE"image3324.tif" INCLUDEPICTURE "D:\\课件\\九数JJ河北（北京）\\image3324.tif" \* MERGEFORMATINET INCLUDEPICTURE "D:\\课件\\九数JJ河北（北京）\\image3324.tif" \* MERGEFORMATINET
A. 　 B.
C. D.
3．用科学计算器计算：＋3tan 56°(结果精确到0.01)．
INCLUDEPICTURE"课堂导学.tif" INCLUDEPICTURE "D:\\课件\\九数JJ河北（北京）\\课堂导学.tif" \* MERGEFORMATINET INCLUDEPICTURE "D:\\课件\\九数JJ河北（北京）\\课堂导学.tif" \* MERGEFORMATINET
INCLUDEPICTURE"W21.tif" INCLUDEPICTURE "D:\\课件\\九数JJ河北（北京）\\W21.tif" \* MERGEFORMATINET INCLUDEPICTURE "D:\\课件\\九数JJ河北（北京）\\W21.tif" \* MERGEFORMATINET
知识点1 用计算器求三角函数值INCLUDEPICTURE"L1.tif" INCLUDEPICTURE "D:\\课件\\九数JJ河北（北京）\\L1.tif" \* MERGEFORMATINET INCLUDEPICTURE "D:\\课件\\九数JJ河北（北京）\\L1.tif" \* MERGEFORMATINET [2023威海一模利用科学计算器计算cos 35°，下列按键顺序正确的是(　　)
A.INCLUDEPICTURE"image3336.tif" INCLUDEPICTURE "D:\\课件\\九数JJ河北（北京）\\image3336.tif" \* MERGEFORMATINET INCLUDEPICTURE "D:\\课件\\九数JJ河北（北京）\\image3336.tif" \* MERGEFORMATINET
B.INCLUDEPICTURE"image3337.tif" INCLUDEPICTURE "D:\\课件\\九数JJ河北（北京）\\image3337.tif" \* MERGEFORMATINET INCLUDEPICTURE "D:\\课件\\九数JJ河北（北京）\\image3337.tif" \* MERGEFORMATINET
C.INCLUDEPICTURE"image3338.tif" INCLUDEPICTURE "D:\\课件\\九数JJ河北（北京）\\image3338.tif" \* MERGEFORMATINET INCLUDEPICTURE "D:\\课件\\九数JJ河北（北京）\\image3338.tif" \* MERGEFORMATINET
D.INCLUDEPICTURE"image3339.tif" INCLUDEPICTURE "D:\\课件\\九数JJ河北（北京）\\image3339.tif" \* MERGEFORMATINET INCLUDEPICTURE "D:\\课件\\九数JJ河北（北京）\\image3339.tif" \* MERGEFORMATINET
变式1用计算器求下列各式的值(结果精确到0.000 1)：
(1)sin 47°；　　(2)sin 12°30′；
(3)cos 25°18′；(4)sin 18°＋cos 55°－tan 59°.
　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　
知识点2 已知三角函数值用计算器求角度
INCLUDEPICTURE"L2.tif" INCLUDEPICTURE "D:\\课件\\九数JJ河北（北京）\\L2.tif" \* MERGEFORMATINET INCLUDEPICTURE "D:\\课件\\九数JJ河北（北京）\\L2.tif" \* MERGEFORMATINET 已知sin A＝0.501 8，用计算器求∠A的度数．(结果精确到1″)
变式2利用我们数学课本上采用的科学计算器按顺序依次输入：，显示屏显示的结果为88.443 009 64.将这个数据精确到0.1后，下列说法正确的是(　　)
A．36.79°的正切函数值约为88.4
B．正切函数值为36.79的角约是88.4°
C．36°79′的正切函数值约为88.4
D．正切函数值为36.79的角约是88°4′
26. 2 锐角三角函数的计算
INCLUDEPICTURE"复习回顾.tif" INCLUDEPICTURE "D:\\课件\\九数JJ河北（北京）\\复习回顾.tif" \* MERGEFORMATINET INCLUDEPICTURE "D:\\课件\\九数JJ河北（北京）\\复习回顾.tif" \* MERGEFORMATINET
1．A　2.C
3.
30° 45° 60°
sinα
cosα
tanα 1
INCLUDEPICTURE"预习效果.tif" INCLUDEPICTURE "预习效果.tif" \* MERGEFORMAT INCLUDEPICTURE "D:\\课件\\九数JJ河北（北京）\\预习效果.tif" \* MERGEFORMATINET INCLUDEPICTURE "D:\\课件\\九数JJ河北（北京）\\预习效果.tif" \* MERGEFORMATINET INCLUDEPICTURE "D:\\课件\\九数JJ河北（北京）\\预习效果.tif" \* MERGEFORMATINET
1．A　2.A
3．解：＋3tan 56°≈5.568＋3×1.483＝5.568＋4.449≈10.02.
INCLUDEPICTURE"课堂导学.tif" INCLUDEPICTURE "课堂导学.tif" \* MERGEFORMAT INCLUDEPICTURE "D:\\课件\\九数JJ河北（北京）\\课堂导学.tif" \* MERGEFORMATINET INCLUDEPICTURE "D:\\课件\\九数JJ河北（北京）\\课堂导学.tif" \* MERGEFORMATINET INCLUDEPICTURE "D:\\课件\\九数JJ河北（北京）\\课堂导学.tif" \* MERGEFORMATINET
例1　A　变式1.解：(1)sin 47°≈0.731 4；
(2)sin 12°30′≈0.216 4；
(3)cos 25°18′≈0.904 1；
(4)sin 18°＋cos 55°－tan 59°≈－0.781 7.
例2　解：利用计算器可求得∠A的度数约为30°7′9″.
变式2.B

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