f（-5）=x5-ax3+bx+2=17;所以x5-ax3+bx=15f（5）=-(x5-ax3+bx)+2=-15+2=-13
-13 f(-5) = 17 推出 -23+15a-5b = 17 也就是15a-5b =40 f(5) = 27-15a+5b = 27-(15a-5b) = 27-40 =-13
好学的孩子
