-.921=.5*-9.8t^2

Solution for -.921=.5*-9.8t^2 equation:

Simplifying
-0.921 = 0.5 * -9.8t2

Multiply 0.5 * -9.8
-0.921 = -4.9t2

Solving
-0.921 = -4.9t2

Solving for variable 't'.

Move all terms containing t to the left, all other terms to the right.

Add '4.9t2' to each side of the equation.
-0.921 + 4.9t2 = -4.9t2 + 4.9t2

Combine like terms: -4.9t2 + 4.9t2 = 0.0
-0.921 + 4.9t2 = 0.0

Add '0.921' to each side of the equation.
-0.921 + 0.921 + 4.9t2 = 0.0 + 0.921

Combine like terms: -0.921 + 0.921 = 0.000
0.000 + 4.9t2 = 0.0 + 0.921
4.9t2 = 0.0 + 0.921

Combine like terms: 0.0 + 0.921 = 0.921
4.9t2 = 0.921

Divide each side by '4.9'.
t2 = 0.1879591837

Simplifying
t2 = 0.1879591837

Take the square root of each side:
t = {-0.433542597, 0.433542597}