x^2+10x+21=400

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Solution for x^2+10x+21=400 equation:


Simplifying
x2 + 10x + 21 = 400

Reorder the terms:
21 + 10x + x2 = 400

Solving
21 + 10x + x2 = 400

Solving for variable 'x'.

Reorder the terms:
21 + -400 + 10x + x2 = 400 + -400

Combine like terms: 21 + -400 = -379
-379 + 10x + x2 = 400 + -400

Combine like terms: 400 + -400 = 0
-379 + 10x + x2 = 0

Begin completing the square.

Move the constant term to the right:

Add '379' to each side of the equation.
-379 + 10x + 379 + x2 = 0 + 379

Reorder the terms:
-379 + 379 + 10x + x2 = 0 + 379

Combine like terms: -379 + 379 = 0
0 + 10x + x2 = 0 + 379
10x + x2 = 0 + 379

Combine like terms: 0 + 379 = 379
10x + x2 = 379

The x term is 10x.  Take half its coefficient (5).
Square it (25) and add it to both sides.

Add '25' to each side of the equation.
10x + 25 + x2 = 379 + 25

Reorder the terms:
25 + 10x + x2 = 379 + 25

Combine like terms: 379 + 25 = 404
25 + 10x + x2 = 404

Factor a perfect square on the left side:
(x + 5)(x + 5) = 404

Calculate the square root of the right side: 20.099751242

Break this problem into two subproblems by setting 
(x + 5) equal to 20.099751242 and -20.099751242.

Subproblem 1

x + 5 = 20.099751242 Simplifying x + 5 = 20.099751242 Reorder the terms: 5 + x = 20.099751242 Solving 5 + x = 20.099751242 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-5' to each side of the equation. 5 + -5 + x = 20.099751242 + -5 Combine like terms: 5 + -5 = 0 0 + x = 20.099751242 + -5 x = 20.099751242 + -5 Combine like terms: 20.099751242 + -5 = 15.099751242 x = 15.099751242 Simplifying x = 15.099751242

Subproblem 2

x + 5 = -20.099751242 Simplifying x + 5 = -20.099751242 Reorder the terms: 5 + x = -20.099751242 Solving 5 + x = -20.099751242 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-5' to each side of the equation. 5 + -5 + x = -20.099751242 + -5 Combine like terms: 5 + -5 = 0 0 + x = -20.099751242 + -5 x = -20.099751242 + -5 Combine like terms: -20.099751242 + -5 = -25.099751242 x = -25.099751242 Simplifying x = -25.099751242

Solution

The solution to the problem is based on the solutions from the subproblems. x = {15.099751242, -25.099751242}

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