5t^2-21t-28=0

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Solution for 5t^2-21t-28=0 equation:


Simplifying
5t2 + -21t + -28 = 0

Reorder the terms:
-28 + -21t + 5t2 = 0

Solving
-28 + -21t + 5t2 = 0

Solving for variable 't'.

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

Divide each side by '5'.
-5.6 + -4.2t + t2 = 0

Move the constant term to the right:

Add '5.6' to each side of the equation.
-5.6 + -4.2t + 5.6 + t2 = 0 + 5.6

Reorder the terms:
-5.6 + 5.6 + -4.2t + t2 = 0 + 5.6

Combine like terms: -5.6 + 5.6 = 0.0
0.0 + -4.2t + t2 = 0 + 5.6
-4.2t + t2 = 0 + 5.6

Combine like terms: 0 + 5.6 = 5.6
-4.2t + t2 = 5.6

The t term is -4.2t.  Take half its coefficient (-2.1).
Square it (4.41) and add it to both sides.

Add '4.41' to each side of the equation.
-4.2t + 4.41 + t2 = 5.6 + 4.41

Reorder the terms:
4.41 + -4.2t + t2 = 5.6 + 4.41

Combine like terms: 5.6 + 4.41 = 10.01
4.41 + -4.2t + t2 = 10.01

Factor a perfect square on the left side:
(t + -2.1)(t + -2.1) = 10.01

Calculate the square root of the right side: 3.163858404

Break this problem into two subproblems by setting 
(t + -2.1) equal to 3.163858404 and -3.163858404.

Subproblem 1

t + -2.1 = 3.163858404 Simplifying t + -2.1 = 3.163858404 Reorder the terms: -2.1 + t = 3.163858404 Solving -2.1 + t = 3.163858404 Solving for variable 't'. Move all terms containing t to the left, all other terms to the right. Add '2.1' to each side of the equation. -2.1 + 2.1 + t = 3.163858404 + 2.1 Combine like terms: -2.1 + 2.1 = 0.0 0.0 + t = 3.163858404 + 2.1 t = 3.163858404 + 2.1 Combine like terms: 3.163858404 + 2.1 = 5.263858404 t = 5.263858404 Simplifying t = 5.263858404

Subproblem 2

t + -2.1 = -3.163858404 Simplifying t + -2.1 = -3.163858404 Reorder the terms: -2.1 + t = -3.163858404 Solving -2.1 + t = -3.163858404 Solving for variable 't'. Move all terms containing t to the left, all other terms to the right. Add '2.1' to each side of the equation. -2.1 + 2.1 + t = -3.163858404 + 2.1 Combine like terms: -2.1 + 2.1 = 0.0 0.0 + t = -3.163858404 + 2.1 t = -3.163858404 + 2.1 Combine like terms: -3.163858404 + 2.1 = -1.063858404 t = -1.063858404 Simplifying t = -1.063858404

Solution

The solution to the problem is based on the solutions from the subproblems. t = {5.263858404, -1.063858404}

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