-40=0+0.5*-9.8*t^2

Solution for -40=0+0.5*-9.8*t^2 equation:

Simplifying
-40 = 0 + 0.5 * -9.8t2

Multiply 0.5 * -9.8
-40 = 0 + -4.9t2
Remove the zero:
-40 = -4.9t2

Solving
-40 = -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.
-40 + 4.9t2 = -4.9t2 + 4.9t2

Combine like terms: -4.9t2 + 4.9t2 = 0.0
-40 + 4.9t2 = 0.0

Add '40' to each side of the equation.
-40 + 40 + 4.9t2 = 0.0 + 40

Combine like terms: -40 + 40 = 0
0 + 4.9t2 = 0.0 + 40
4.9t2 = 0.0 + 40

Combine like terms: 0.0 + 40 = 40
4.9t2 = 40

Divide each side by '4.9'.
t2 = 8.163265306

Simplifying
t2 = 8.163265306

Take the square root of each side:
t = {-2.857142857, 2.857142857}