You use the quadratic formula.
x1 =
- (-28) - the square root of (-28) to the power of 2 minus 4 times 1 times 3 divided by 2 x 1 =
28 - 2 x the square root of 193 divided by 2 is 0.108.
x2 =
- (-28) plus the square root of (-28) to the power of 2 minus 4 times 1 times 3 divided by 2 times 1 =
28 plus 2 times the square root of 193 divided by 2 is 27.892
Extrema:
Min would equal (14, -193)