辽宁省营口市2017届中考模拟数学试卷(2)含答案

·········· (4 分) (2) 是直径, . . 又,, . ····················································································· (5 分) 又,.(8 分) (3),. 东(钓鱼岛) 北 PBA 30 o 75 o ,. ··················································· ( 10 分) 设,则. 又,. 解之,得,.,. ∴ BC=AC=4 又∵ OC=3 ∴ OA=5 ································································· ( 12 分) 23 (1) 解:(1)∵甲车途径 C地时休息一小时, ∴ 2.5 ﹣ m=1 , ∴ m=1.5 , 乙车的速度==, 即=60 , 解得 a=90 , 甲车的速度为: =, 解得 n=3.5 ; 所以, a=90 , m=1.5 , n=3.5 ; (2)设甲车的 y与x的函数关系式为 y=kx+b (k≠0), ①休息前, 0≤x< 1.5 ,函数图象经过点( 0, 300 )和( 1.5 , 120 ), 所以, , 解得, 所以, y=﹣ 120x+300 , ②休息时, 1.5 ≤x< 2.5 , y=120 , ③休息后, 2.5 ≤x≤ 3.5 ,函数图象经过( 2.5 , 120 )和( 3.5 ,0), 所以, , 解得, 所以, y=﹣ 120x+420 . 综上, y与x的关系式为 y=; (3)设两车相距 120 千米时,乙车行驶了 x小时, 甲车的速度为:( 300 ﹣ 120 )÷ 1.5=120 千米/时, ①若相遇前,则 120x+60x=300 ﹣ 120 ,