△＝b²-4ac
=6²-4×3×(-5)
=36+60
=96
所以：
x1=(-b+√b²-4ac)/2a
=(-6+4√6)/6
=-(3-2√6)/3
x2=(-b-√b²-4ac)/2a
=(-6-4√6)/6
=-(3+2√6)/3