2t^2-9t-21=0

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Solution for 2t^2-9t-21=0 equation:


Simplifying
2t2 + -9t + -21 = 0

Reorder the terms:
-21 + -9t + 2t2 = 0

Solving
-21 + -9t + 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 + -4.5t + t2 = 0

Move the constant term to the right:

Add '10.5' to each side of the equation.
-10.5 + -4.5t + 10.5 + t2 = 0 + 10.5

Reorder the terms:
-10.5 + 10.5 + -4.5t + t2 = 0 + 10.5

Combine like terms: -10.5 + 10.5 = 0.0
0.0 + -4.5t + t2 = 0 + 10.5
-4.5t + t2 = 0 + 10.5

Combine like terms: 0 + 10.5 = 10.5
-4.5t + t2 = 10.5

The t term is -4.5t.  Take half its coefficient (-2.25).
Square it (5.0625) and add it to both sides.

Add '5.0625' to each side of the equation.
-4.5t + 5.0625 + t2 = 10.5 + 5.0625

Reorder the terms:
5.0625 + -4.5t + t2 = 10.5 + 5.0625

Combine like terms: 10.5 + 5.0625 = 15.5625
5.0625 + -4.5t + t2 = 15.5625

Factor a perfect square on the left side:
(t + -2.25)(t + -2.25) = 15.5625

Calculate the square root of the right side: 3.94493346

Break this problem into two subproblems by setting 
(t + -2.25) equal to 3.94493346 and -3.94493346.

Subproblem 1

t + -2.25 = 3.94493346 Simplifying t + -2.25 = 3.94493346 Reorder the terms: -2.25 + t = 3.94493346 Solving -2.25 + t = 3.94493346 Solving for variable 't'. Move all terms containing t to the left, all other terms to the right. Add '2.25' to each side of the equation. -2.25 + 2.25 + t = 3.94493346 + 2.25 Combine like terms: -2.25 + 2.25 = 0.00 0.00 + t = 3.94493346 + 2.25 t = 3.94493346 + 2.25 Combine like terms: 3.94493346 + 2.25 = 6.19493346 t = 6.19493346 Simplifying t = 6.19493346

Subproblem 2

t + -2.25 = -3.94493346 Simplifying t + -2.25 = -3.94493346 Reorder the terms: -2.25 + t = -3.94493346 Solving -2.25 + t = -3.94493346 Solving for variable 't'. Move all terms containing t to the left, all other terms to the right. Add '2.25' to each side of the equation. -2.25 + 2.25 + t = -3.94493346 + 2.25 Combine like terms: -2.25 + 2.25 = 0.00 0.00 + t = -3.94493346 + 2.25 t = -3.94493346 + 2.25 Combine like terms: -3.94493346 + 2.25 = -1.69493346 t = -1.69493346 Simplifying t = -1.69493346

Solution

The solution to the problem is based on the solutions from the subproblems. t = {6.19493346, -1.69493346}

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