求教xdf补充材料510,534

efficiency

510: what is the 1st term in sequence S?

1.the 3rd term is 2

2. the 2nd term is twice the 1st, and the 3rd term is 3 times the 2nd

为什么不是C?

534.If the number of square units in the area of a circle is A and the number of linear units in the circumference is C, what is the radius of the circle?

1. A/c=1.5

2. A>C+3

其中的square units 和linear units何解?

多谢!

himba

510:

这个应该是C吧。

条件1不知道S各项之间的关系，单独不充分。

条件2，不知道具体的一项的数字，单独不充分。

条件1加2正好可以算出1ST。

a3=2=3a2,a2=2a1---->a3=6a1-->a1=2/6=1/3.