-8t^2+2t+21=0

Solution for -8t^2+2t+21=0 equation:

Simplifying
-8t2 + 2t + 21 = 0

Reorder the terms:
21 + 2t + -8t2 = 0

Solving
21 + 2t + -8t2 = 0

Solving for variable 't'.

Factor a trinomial.
(7 + -4t)(3 + 2t) = 0

Subproblem 1
Set the factor '(7 + -4t)' equal to zero and attempt to solve:

Simplifying
7 + -4t = 0

Solving
7 + -4t = 0

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

Add '-7' to each side of the equation.
7 + -7 + -4t = 0 + -7

Combine like terms: 7 + -7 = 0
0 + -4t = 0 + -7
-4t = 0 + -7

Combine like terms: 0 + -7 = -7
-4t = -7

Divide each side by '-4'.
t = 1.75

Simplifying
t = 1.75
Subproblem 2
Set the factor '(3 + 2t)' equal to zero and attempt to solve:

Simplifying
3 + 2t = 0

Solving
3 + 2t = 0

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

Add '-3' to each side of the equation.
3 + -3 + 2t = 0 + -3

Combine like terms: 3 + -3 = 0
0 + 2t = 0 + -3
2t = 0 + -3

Combine like terms: 0 + -3 = -3
2t = -3

Divide each side by '2'.
t = -1.5

Simplifying
t = -1.5
Solution
t = {1.75, -1.5}