The value of the expression when a=3 and b=4 is 15.59.
The expression given is a quadratic equation of the form at² + bt + c = 0, where the constants are a = 3, b = 4, and c = 3.59.
To find the value of the expression, we substitute the given values of a and b into the equation:
a x b + c = 3 x 4 + 3.59
= 12 + 3.59
= 15.59
Therefore, the value of the expression when a = 3 and b = 4 is 15.59.