2.5=(2)t+(.5)(-9.8)t^2

Solution for 2.5=(2)t+(.5)(-9.8)t^2 equation:

Simplifying
2.5 = (2) * t + (0.5)(-9.8) * t2

Multiply 0.5 * -9.8
2.5 = 2t + -4.9t2

Solving
2.5 = 2t + -4.9t2

Solving for variable 't'.

Reorder the terms:
2.5 + -2t + 4.9t2 = 2t + -2t + -4.9t2 + 4.9t2

Combine like terms: 2t + -2t = 0
2.5 + -2t + 4.9t2 = 0 + -4.9t2 + 4.9t2
2.5 + -2t + 4.9t2 = -4.9t2 + 4.9t2

Combine like terms: -4.9t2 + 4.9t2 = 0.0
2.5 + -2t + 4.9t2 = 0.0

Begin completing the square.  Divide all terms by
4.9 the coefficient of the squared term: 

Divide each side by '4.9'.
0.5102040816 + -0.4081632653t + t2 = 0

Move the constant term to the right:

Add '-0.5102040816' to each side of the equation.
0.5102040816 + -0.4081632653t + -0.5102040816 + t2 = 0 + -0.5102040816

Reorder the terms:
0.5102040816 + -0.5102040816 + -0.4081632653t + t2 = 0 + -0.5102040816

Combine like terms: 0.5102040816 + -0.5102040816 = 0.0000000000
0.0000000000 + -0.4081632653t + t2 = 0 + -0.5102040816
-0.4081632653t + t2 = 0 + -0.5102040816

Combine like terms: 0 + -0.5102040816 = -0.5102040816
-0.4081632653t + t2 = -0.5102040816

The t term is -0.4081632653t.  Take half its coefficient (-0.2040816327).
Square it (0.04164931281) and add it to both sides.

Add '0.04164931281' to each side of the equation.
-0.4081632653t + 0.04164931281 + t2 = -0.5102040816 + 0.04164931281

Reorder the terms:
0.04164931281 + -0.4081632653t + t2 = -0.5102040816 + 0.04164931281

Combine like terms: -0.5102040816 + 0.04164931281 = -0.46855476879
0.04164931281 + -0.4081632653t + t2 = -0.46855476879

Factor a perfect square on the left side:
(t + -0.2040816327)(t + -0.2040816327) = -0.46855476879

Can't calculate square root of the right side.

The solution to this equation could not be determined.