在RT三角形ABC中,角ACB=90度,AB=10,BC=8,点D在BC上运动(不运动至B,C)DE//CA,交AB于E,设BD为X,三角形ADE的面积为Y
1.求函数表达式和X的取值范围
2.三角形ABC的面积何时最大,是多少
3,当TAN角ECA=4,三角形ADE的面积?
人气：328 ℃ 时间：2019-08-18 02:48:45
解答
过D做DM⊥ABDE‖AC,x：BC=BE：AB,BE=5/4x,AE=10-5/4x△DMB∽△ACB,DM：6=x：10,DM=3/5xy=1/2×AE×DM==3x-3/8x²（0＜x＜8）2、y=3x-3/8x²=-3/8（x-4）²+6,x=4时最大,为63、∠ECA=∠CED,tanECA=4,tanC...
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