中四Math .....一問

Since 5x^2 + 3x + (k+1) = 0 has two distinct roots
b^2 - 4ac > 0

In this case, a=5, b=3, c=k+1
==> 3^2 - 4(5)(k+1) > 0
9 - 20(k+1) > 0
9 - 20k - 20 > 0
-11 - 20k > 0
-20k > 11
k < 11/(-20) <== Be noted that if the coefficient of k is negative, we must change the ">" to the opposite sign "<" !!!! If forget the answer is wrong!

Therefore k < -11/20

discriminants=9-4(5)(k+1)>0
20(k+1)<9
k<9/20-1
∴k<-11/20