r^2+2r-77=

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Solution for r^2+2r-77= equation:


Simplifying
r2 + 2r + -77 = 0

Reorder the terms:
-77 + 2r + r2 = 0

Solving
-77 + 2r + r2 = 0

Solving for variable 'r'.

Begin completing the square.

Move the constant term to the right:

Add '77' to each side of the equation.
-77 + 2r + 77 + r2 = 0 + 77

Reorder the terms:
-77 + 77 + 2r + r2 = 0 + 77

Combine like terms: -77 + 77 = 0
0 + 2r + r2 = 0 + 77
2r + r2 = 0 + 77

Combine like terms: 0 + 77 = 77
2r + r2 = 77

The r term is 2r.  Take half its coefficient (1).
Square it (1) and add it to both sides.

Add '1' to each side of the equation.
2r + 1 + r2 = 77 + 1

Reorder the terms:
1 + 2r + r2 = 77 + 1

Combine like terms: 77 + 1 = 78
1 + 2r + r2 = 78

Factor a perfect square on the left side:
(r + 1)(r + 1) = 78

Calculate the square root of the right side: 8.831760866

Break this problem into two subproblems by setting 
(r + 1) equal to 8.831760866 and -8.831760866.

Subproblem 1

r + 1 = 8.831760866 Simplifying r + 1 = 8.831760866 Reorder the terms: 1 + r = 8.831760866 Solving 1 + r = 8.831760866 Solving for variable 'r'. Move all terms containing r to the left, all other terms to the right. Add '-1' to each side of the equation. 1 + -1 + r = 8.831760866 + -1 Combine like terms: 1 + -1 = 0 0 + r = 8.831760866 + -1 r = 8.831760866 + -1 Combine like terms: 8.831760866 + -1 = 7.831760866 r = 7.831760866 Simplifying r = 7.831760866

Subproblem 2

r + 1 = -8.831760866 Simplifying r + 1 = -8.831760866 Reorder the terms: 1 + r = -8.831760866 Solving 1 + r = -8.831760866 Solving for variable 'r'. Move all terms containing r to the left, all other terms to the right. Add '-1' to each side of the equation. 1 + -1 + r = -8.831760866 + -1 Combine like terms: 1 + -1 = 0 0 + r = -8.831760866 + -1 r = -8.831760866 + -1 Combine like terms: -8.831760866 + -1 = -9.831760866 r = -9.831760866 Simplifying r = -9.831760866

Solution

The solution to the problem is based on the solutions from the subproblems. r = {7.831760866, -9.831760866}

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