为奇函数 ············································(4分)
(2)函数在(-1,1)为单调增函数.证明如下:
任取,则
····························(6分)
, ······························(7分) ,即·······························(8分)
故在(-1,1)上为增函数····································(9分)
(3)由(1),(2)可得
则 解得: ∴原不等式的解集为{x|0
21.(12分)解:(1)由图可知"A" ("0,20" ),"B" ("25,45" ),"C" ("25,75" ),"D" ("30,70" ),设"AB" 所在直线方程为P=kt+20,把"B" ("25,45" )代入P=kt+20得"k=1" ,所以. l_AB:P=t+20,··(1分)
设"CD" 所在的直线方程为P-75=(75-70)/(25-30) (t-25),即P=-t+100,25≤x≤30,··(2分)
所以P={█(t+20,0
(2)由题意,设Q=k_1 t+b,把两点(5,35),(15,25)代入得{█(5k_1+b=35@15k_1+b=25) ,
解得{█(k_1=-1@b=40) 所以Q=-t+40,把点(20,20),(30,10)代入Q=-t+40也适合, (6分)
所以Q=-t+40(0
(3)设日销售金额为y,依题意得,