1、S=,T=。One number is selected from S, and the other number is selected from T. What is the probability that the product of the two numbers is negative?
【答案】/2
【思路】C5 C3 / C5 C6 =/2
2、
What is the function of the curve above?
y = x^3 - x^2
y = - x^3 + x^2
y = - x^3 +x
y = x^3 - x
y = x^3 + x
【答案】
【思路】根據圖形可以知道應該找與X軸有三個交點,也就是y等於0時可以解出三個實根的'方程。排除、、,因為只有兩個實根,也是有兩個實根,只有一個實根,只有是對的。又可以通過增減函式來排除,圖形告訴我們X向正無窮方向增加,Y的值也隨之增加,從某點開始為增函式,再看方程明顯從某點開始後為減函式,因此是對的。
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3、0-50中,被3整除餘的數有多少個?
【答案】有7個
【思路】0=3x+=50 x=0.6
4、N is the sum of the first K consecutive positive integers, where 0=50. What is the sum of /N?
【答案】2
【思路】把first consecutive 理解為是從開始到k 的數列。
N=K/2