5x(x+5)-21=

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Solution for 5x(x+5)-21= equation:


Simplifying
5x(x + 5) + -21 = 0

Reorder the terms:
5x(5 + x) + -21 = 0
(5 * 5x + x * 5x) + -21 = 0
(25x + 5x2) + -21 = 0

Reorder the terms:
-21 + 25x + 5x2 = 0

Solving
-21 + 25x + 5x2 = 0

Solving for variable 'x'.

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

Divide each side by '5'.
-4.2 + 5x + x2 = 0

Move the constant term to the right:

Add '4.2' to each side of the equation.
-4.2 + 5x + 4.2 + x2 = 0 + 4.2

Reorder the terms:
-4.2 + 4.2 + 5x + x2 = 0 + 4.2

Combine like terms: -4.2 + 4.2 = 0.0
0.0 + 5x + x2 = 0 + 4.2
5x + x2 = 0 + 4.2

Combine like terms: 0 + 4.2 = 4.2
5x + x2 = 4.2

The x term is 5x.  Take half its coefficient (2.5).
Square it (6.25) and add it to both sides.

Add '6.25' to each side of the equation.
5x + 6.25 + x2 = 4.2 + 6.25

Reorder the terms:
6.25 + 5x + x2 = 4.2 + 6.25

Combine like terms: 4.2 + 6.25 = 10.45
6.25 + 5x + x2 = 10.45

Factor a perfect square on the left side:
(x + 2.5)(x + 2.5) = 10.45

Calculate the square root of the right side: 3.232645975

Break this problem into two subproblems by setting 
(x + 2.5) equal to 3.232645975 and -3.232645975.

Subproblem 1

x + 2.5 = 3.232645975 Simplifying x + 2.5 = 3.232645975 Reorder the terms: 2.5 + x = 3.232645975 Solving 2.5 + x = 3.232645975 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-2.5' to each side of the equation. 2.5 + -2.5 + x = 3.232645975 + -2.5 Combine like terms: 2.5 + -2.5 = 0.0 0.0 + x = 3.232645975 + -2.5 x = 3.232645975 + -2.5 Combine like terms: 3.232645975 + -2.5 = 0.732645975 x = 0.732645975 Simplifying x = 0.732645975

Subproblem 2

x + 2.5 = -3.232645975 Simplifying x + 2.5 = -3.232645975 Reorder the terms: 2.5 + x = -3.232645975 Solving 2.5 + x = -3.232645975 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-2.5' to each side of the equation. 2.5 + -2.5 + x = -3.232645975 + -2.5 Combine like terms: 2.5 + -2.5 = 0.0 0.0 + x = -3.232645975 + -2.5 x = -3.232645975 + -2.5 Combine like terms: -3.232645975 + -2.5 = -5.732645975 x = -5.732645975 Simplifying x = -5.732645975

Solution

The solution to the problem is based on the solutions from the subproblems. x = {0.732645975, -5.732645975}

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