(2012•宿迁)-5的相反数是 .
考点分析:
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(2002•三明)如果收入5元记作+5元,那么支出3元记作
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(2002•宜昌)小红家为购买化肥、农药,共支出了200元,记作-200元,那么小红家卖出农产品后获得的收入800元应记作
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(2002•扬州)下列说法:①
![manfen5.com 满分网](http://img.manfen5.com/res/CZSX/web/STSource/20131021232449800347465/SYS201310212324498003474004_ST/0.png)
是有理数;②30476保留三个有效数字的近似值为3.05×10
4;③
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是最简二次根式;④直线y=-2x+3不经过第三象限.其中说法正确的有( )
A.1个
B.2个
C.3个
D.4个
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(2002•十堰)下列各题中解题方法或说法正确的个数有( )
(1)用换元法解方程
![manfen5.com 满分网](http://img.manfen5.com/res/CZSX/web/STSource/20131021232449800347465/SYS201310212324498003474003_ST/0.png)
+
![manfen5.com 满分网](http://img.manfen5.com/res/CZSX/web/STSource/20131021232449800347465/SYS201310212324498003474003_ST/1.png)
+3=0,设
![manfen5.com 满分网](http://img.manfen5.com/res/CZSX/web/STSource/20131021232449800347465/SYS201310212324498003474003_ST/2.png)
=y,则原方程可化为y+
![manfen5.com 满分网](http://img.manfen5.com/res/CZSX/web/STSource/20131021232449800347465/SYS201310212324498003474003_ST/3.png)
+3=0;
(2)若x+y=a,x-y=b,求2x
2+2y
2的值.用配方法求,2x
2+2y
2=(x+y)
2+(x-y)
2;
(3)若x
2-4x+4+
![manfen5.com 满分网](http://img.manfen5.com/res/CZSX/web/STSource/20131021232449800347465/SYS201310212324498003474003_ST/4.png)
=0,求x、y的值.用非负数的和为零解,则原式可以化为(x-2)
2+
![manfen5.com 满分网](http://img.manfen5.com/res/CZSX/web/STSource/20131021232449800347465/SYS201310212324498003474003_ST/5.png)
=0;
(4)四个全等的任意四边形的地砖,铺成一片可以不留空隙.
A.1个
B.2个
C.3个
D.4个
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