x^2+21x-98=0

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Solution for x^2+21x-98=0 equation:


Simplifying
x2 + 21x + -98 = 0

Reorder the terms:
-98 + 21x + x2 = 0

Solving
-98 + 21x + x2 = 0

Solving for variable 'x'.

Begin completing the square.

Move the constant term to the right:

Add '98' to each side of the equation.
-98 + 21x + 98 + x2 = 0 + 98

Reorder the terms:
-98 + 98 + 21x + x2 = 0 + 98

Combine like terms: -98 + 98 = 0
0 + 21x + x2 = 0 + 98
21x + x2 = 0 + 98

Combine like terms: 0 + 98 = 98
21x + x2 = 98

The x term is 21x.  Take half its coefficient (10.5).
Square it (110.25) and add it to both sides.

Add '110.25' to each side of the equation.
21x + 110.25 + x2 = 98 + 110.25

Reorder the terms:
110.25 + 21x + x2 = 98 + 110.25

Combine like terms: 98 + 110.25 = 208.25
110.25 + 21x + x2 = 208.25

Factor a perfect square on the left side:
(x + 10.5)(x + 10.5) = 208.25

Calculate the square root of the right side: 14.43086969

Break this problem into two subproblems by setting 
(x + 10.5) equal to 14.43086969 and -14.43086969.

Subproblem 1

x + 10.5 = 14.43086969 Simplifying x + 10.5 = 14.43086969 Reorder the terms: 10.5 + x = 14.43086969 Solving 10.5 + x = 14.43086969 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-10.5' to each side of the equation. 10.5 + -10.5 + x = 14.43086969 + -10.5 Combine like terms: 10.5 + -10.5 = 0.0 0.0 + x = 14.43086969 + -10.5 x = 14.43086969 + -10.5 Combine like terms: 14.43086969 + -10.5 = 3.93086969 x = 3.93086969 Simplifying x = 3.93086969

Subproblem 2

x + 10.5 = -14.43086969 Simplifying x + 10.5 = -14.43086969 Reorder the terms: 10.5 + x = -14.43086969 Solving 10.5 + x = -14.43086969 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-10.5' to each side of the equation. 10.5 + -10.5 + x = -14.43086969 + -10.5 Combine like terms: 10.5 + -10.5 = 0.0 0.0 + x = -14.43086969 + -10.5 x = -14.43086969 + -10.5 Combine like terms: -14.43086969 + -10.5 = -24.93086969 x = -24.93086969 Simplifying x = -24.93086969

Solution

The solution to the problem is based on the solutions from the subproblems. x = {3.93086969, -24.93086969}

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