8.下列从左到右的变形中,是分解因式的是( )
| A. | a2-4a+5=a(a-4)+5 | B. | (x+2)(x+3)=x2+5x+6 | C. | a2-9b2=(a+3b)(a-3b) | D. | x+1=x(1+$\frac{1}{x}$) |
4.
程程和小宁去商店买笔,程程买的是2元/支的A型笔,小宁买的是2.5元/支的B型笔,设程程买了x支A型笔,小宁买了y支B型笔,根据图中两人的对话,可列方程组为( )
| A. | $\left\{\begin{array}{l}{x-y=2}\\{2.5x+2y=17.5}\end{array}\right.$ | B. | $\left\{\begin{array}{l}{x-y=2}\\{2x+2.5y=17.5}\end{array}\right.$ | ||
| C. | $\left\{\begin{array}{l}{y-x=2}\\{2x+2.5y=17.5}\end{array}\right.$ | D. | $\left\{\begin{array}{l}{x+y=2}\\{2.5x+2y=17.5}\end{array}\right.$ |
2.下列计算正确的是( )
0 285017 285025 285031 285035 285041 285043 285047 285053 285055 285061 285067 285071 285073 285077 285083 285085 285091 285095 285097 285101 285103 285107 285109 285111 285112 285113 285115 285116 285117 285119 285121 285125 285127 285131 285133 285137 285143 285145 285151 285155 285157 285161 285167 285173 285175 285181 285185 285187 285193 285197 285203 285211 366461
| A. | (x2)4=x6 | B. | m2+m4=m6 | C. | a2•a3=a6 | D. | (-3x3)2=9x6 |