abcd=24
1×2×3×4=24,a+b+c+d=10
(-1)×(-2)×3×4=24,a+b+c+d=4
(-1)×2×(-3)×4=24,a+b+c+d=2
(-1)×2×3×(-4)=24,a+b+c+d=0
1×(-2)×(-3)×4=24,a+b+c+d=0
1×(-2)×3×(-4)=24,a+b+c+d=-2
1×2×(-3)×(-4)=24,a+b+c+d=-4
(-1)×(-2)×(-3)×(-4)=24,a+b+c+d=-10
a+b+c+d∈{-10,-4,-2,0,2,4,10}