13.下列各式的分解因式中,没有用到公式法的是( )
| A. | 3m2-6mn+3n2=3(m-n)2 | B. | x2b+ab2+ab=ab(a+b+1) | ||
| C. | mx2-4m=m(x-2)(x+2) | D. | x2+12x+36=(x+6)2 |
12.
如图所示,弹簧不挂重物时的长度是( )
| A. | 9cm | B. | 10cm | C. | 10.5cm | D. | 11cm |
10.甲、乙两人在400米的环形跑道上练习跑步,若同向跑,甲a分钟可超乙一圈;若反向跑,两人每隔b分钟相遇一次,则甲、乙速度之比为( )
0 286844 286852 286858 286862 286868 286870 286874 286880 286882 286888 286894 286898 286900 286904 286910 286912 286918 286922 286924 286928 286930 286934 286936 286938 286939 286940 286942 286943 286944 286946 286948 286952 286954 286958 286960 286964 286970 286972 286978 286982 286984 286988 286994 287000 287002 287008 287012 287014 287020 287024 287030 287038 366461
| A. | $\frac{a+400}{b+400}$ | B. | $\frac{a}{a+b}$ | C. | $\frac{a+b}{b}$ | D. | $\frac{a+b}{a-b}$ |