3.若a+b=2,则代数式a2-b2+4b的值是( )
| A. | 2 | B. | 4 | C. | -2 | D. | -4 |
2.已知二次函数y=ax2+bx+c自变量x与函数值y之间满足下列数量关系,那么(a+b+c)($\frac{-b+\sqrt{{b}^{2}-4ac}}{2a}$+$\frac{-b-\sqrt{{b}^{2}-4ac}}{2a}$)的值是24.
| x | 3 | 5 | 7 |
| y | 0.08 | 0.08 | 3 |
1.
如图,在△ABC中,AB=AC=10,BC=16,D是边BC上一动点(不与点B,C重合),∠ADE=∠B=α,DE交AC于点E,给出下列结论:①图中有2对相似三角形;②线段CE长的最大值为6.4;③当AD=DC时,BD的长为$\frac{39}{4}$.其中正确的结论是( )
| A. | ①② | B. | ②③ | C. | ①③ | D. | ①②③ |
20.无论a取何值,下列代数式的值总是正数的有( )
|a+1|,a2+3,a+100,|a|+1,a2n+1(n是整数)
|a+1|,a2+3,a+100,|a|+1,a2n+1(n是整数)
| A. | 1个 | B. | 2个 | C. | 3个 | D. | 4个 |
19.下列计算正确的是( )
0 292962 292970 292976 292980 292986 292988 292992 292998 293000 293006 293012 293016 293018 293022 293028 293030 293036 293040 293042 293046 293048 293052 293054 293056 293057 293058 293060 293061 293062 293064 293066 293070 293072 293076 293078 293082 293088 293090 293096 293100 293102 293106 293112 293118 293120 293126 293130 293132 293138 293142 293148 293156 366461
| A. | a4b-6a3b+9a2b=a2b(a2-6a+9) | B. | x2-2x+1=(x-1)2 | ||
| C. | x2-2x+4=(x-2)2 | D. | 4x2-y2=(4x+y)(4x-y) |