已知等差數列{an}中，a1,a10是方程3x^2+6x+1=0的兩個根，則a4+a7的值是 （ ）A.0B.2C.-2D.1請寫出步驟
C解：a4+a7=a1+3d+a1+6d=a1+a1+9d=a1+a10=-2
等差數列{an}中,a4+a7=a1+a10=-2
Ca4+a7=a1+3d+a1+6d=a1+a1+9d=a1+a10=-2
