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已知等腰三角形ABC内接于半径为5的⊙O中,如果底边BC的长为8,那么底角的正切...
已知等腰三角形ABC内接于半径为5的⊙O中,如果底边BC的长为8,那么底角的正切值是 .
考点分析:
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如图,△ABC中,∠ACB=90°,∠B=30°,以C为圆心,CA为半径的圆交AB于D点,若AC=6,则
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的长为
.
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已知:
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(n=1,2,3,…),记b
1=2(1-a
1),b
2=2(1-a
1)(1-a
2),…,b
n=2(1-a
1)(1-a
2)…(1-a
n),则通过计算推测出b
n的表达式b
n=
.(用含n的代数式表示)
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观察下列各式:1=1
2,1+3=4=2
2,1+3+5=9=3
2…根据观察到的规律可得1+3+5+7+…+99=
.
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观察下列计算:
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•(
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+1)=(
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-1)(
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+1)=1,
(
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+
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)(
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+1)=[(
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-1)+(
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-
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)](
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+1)=2,
(
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+
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+
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)(
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+1)=[(
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-1)+(
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-
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)+(
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-
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)](
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+1)=3,
…
从以上计算过程中找出规律,并利用这一规律进行计算:
(
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+
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+
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+…+
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)(
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+1)的值为( )
A.2008
B.2010
C.2011
D.2009
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直线l
1:y=k
1x+b与直线l
2:y=k
2x+c在同一平面直角坐标系中的图象如图所示,则关于x的不等式k
1x+b<k
2x+c的解集为( )
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A.x>1
B.x<1
C.x>-2
D.x<-2
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