10x^2+11x+310x2+11x+3 is of the form ax^2+bx+cax2+bx+c with a=10a=10, b=11b=11 and c=3c=3, so we can calculate the discriminant as follows:
Delta = b^2-4ac = 11^2 - (4xx10xx3) = 121 - 120 = 1 = 1^2
...a positive perfect square. So 10x^2+11x+3 has two distinct rational roots, given by the formula:
x = (-b+-sqrt(Delta))/(2a) = (-11+-1)/20
That is x = -12/20 = -3/5 and x = -10/20 = -1/2
Since x = -3/5 is a root, (5x+3) must be a factor.
Since x = -1/2 is a root, (2x+1) is the other factor.
So 10x^2+11x+3 = (5x+3)(2x+1)