Question

SAT og 3道数学题，帮忙～各位

the total daily cost c,in dollars ,of producing x units of a certain prduct is given by the function c(x)5(600x-200)/x1k,where k is a constant and x#100.if 20 units were prducud yesterday for a total cost of $5640,what is the value of k?怎么也看不懂这个函数和一些符号啊～～

any 2 point determine a line.if there are 6 point in a plain ,no 3 of which lie on the same line.how many lines are determined by pairs of these 6 point?

on a square gameboard that is diveded into n rows of n squares each. k of these squares lie along the boudary of the gameboard. which of the following is a possible value for k?
A 10
B 25
C 34
D 42
E 52

3道题比较多，有会的牛人帮下忙哈，实在是解不出来～～谢谢哦！

Answer 1

第一题。C(x)是一个含有x的方程，x是制造的数量，通过方程，每个固定的x数 会给我们一个固定的c(x)——方程的解&只在x个产品的话费。 现在题目告诉了你，要制造20葛产品 需要话费5640元。所以用5640代替c(x)，20代替x。就可以求出k是多少。（你等式打错了，看不懂..你就自己求吧）

第二题。同一平面上有六个点，同一条直线上只会有期中的两个点，所以答案是15.

第三题。切割一个正方形，横向的正方形数跟纵向的是一样的。所以外围的正方形数一定要是4的倍数。答案是E

希望能帮到你 X)