2.古希腊数学家把数1,3,6,10,15,21,…叫做三角数,它有一定的规律性.若把第一个三角数记为a1,第二个三角数记为a2,…,第n个三角数记为an,则an-1+an=( )( )
| A. | (n-1)2 | B. | n2 | C. | (n+1)2 | D. | (n+2)2 |
1.
如图,△ABC和△AMN都是等边三角形,点M是△ABC的重心,那么$\frac{{S}_{△AMN}}{{S}_{△ABC}}$的值为( )
| A. | $\frac{2}{3}$ | B. | $\frac{1}{3}$ | C. | $\frac{1}{4}$ | D. | $\frac{4}{9}$ |
18.下列运算结果中是正数的是( )
| A. | (-$\frac{1}{2016}$)-1 | B. | -($\frac{1}{2016}$)-2 | C. | -(-$\frac{1}{2016}$)0 | D. | ($\frac{1}{2016}$)-1÷(2016)-1 |
17.下列不等式组无解的是( )
0 283099 283107 283113 283117 283123 283125 283129 283135 283137 283143 283149 283153 283155 283159 283165 283167 283173 283177 283179 283183 283185 283189 283191 283193 283194 283195 283197 283198 283199 283201 283203 283207 283209 283213 283215 283219 283225 283227 283233 283237 283239 283243 283249 283255 283257 283263 283267 283269 283275 283279 283285 283293 366461
| A. | $\left\{\begin{array}{l}{x+1<0}\\{x-2>0}\end{array}\right.$ | B. | $\left\{\begin{array}{l}{x-1<0}\\{x+2>0}\end{array}\right.$ | C. | $\left\{\begin{array}{l}{x+1>0}\\{x-2>0}\end{array}\right.$ | D. | $\left\{\begin{array}{l}{x-2<0}\\{x+1<0}\end{array}\right.$ |