2t^2+8t-21=0

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


Simplifying
2t2 + 8t + -21 = 0

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

Solving
-21 + 8t + 2t2 = 0

Solving for variable 't'.

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

Divide each side by '2'.
-10.5 + 4t + t2 = 0

Move the constant term to the right:

Add '10.5' to each side of the equation.
-10.5 + 4t + 10.5 + t2 = 0 + 10.5

Reorder the terms:
-10.5 + 10.5 + 4t + t2 = 0 + 10.5

Combine like terms: -10.5 + 10.5 = 0.0
0.0 + 4t + t2 = 0 + 10.5
4t + t2 = 0 + 10.5

Combine like terms: 0 + 10.5 = 10.5
4t + t2 = 10.5

The t term is 4t.  Take half its coefficient (2).
Square it (4) and add it to both sides.

Add '4' to each side of the equation.
4t + 4 + t2 = 10.5 + 4

Reorder the terms:
4 + 4t + t2 = 10.5 + 4

Combine like terms: 10.5 + 4 = 14.5
4 + 4t + t2 = 14.5

Factor a perfect square on the left side:
(t + 2)(t + 2) = 14.5

Calculate the square root of the right side: 3.807886553

Break this problem into two subproblems by setting 
(t + 2) equal to 3.807886553 and -3.807886553.

Subproblem 1

t + 2 = 3.807886553 Simplifying t + 2 = 3.807886553 Reorder the terms: 2 + t = 3.807886553 Solving 2 + t = 3.807886553 Solving for variable 't'. Move all terms containing t to the left, all other terms to the right. Add '-2' to each side of the equation. 2 + -2 + t = 3.807886553 + -2 Combine like terms: 2 + -2 = 0 0 + t = 3.807886553 + -2 t = 3.807886553 + -2 Combine like terms: 3.807886553 + -2 = 1.807886553 t = 1.807886553 Simplifying t = 1.807886553

Subproblem 2

t + 2 = -3.807886553 Simplifying t + 2 = -3.807886553 Reorder the terms: 2 + t = -3.807886553 Solving 2 + t = -3.807886553 Solving for variable 't'. Move all terms containing t to the left, all other terms to the right. Add '-2' to each side of the equation. 2 + -2 + t = -3.807886553 + -2 Combine like terms: 2 + -2 = 0 0 + t = -3.807886553 + -2 t = -3.807886553 + -2 Combine like terms: -3.807886553 + -2 = -5.807886553 t = -5.807886553 Simplifying t = -5.807886553

Solution

The solution to the problem is based on the solutions from the subproblems. t = {1.807886553, -5.807886553}

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