7r^2-14r-87=9

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Solution for 7r^2-14r-87=9 equation:


Simplifying
7r2 + -14r + -87 = 9

Reorder the terms:
-87 + -14r + 7r2 = 9

Solving
-87 + -14r + 7r2 = 9

Solving for variable 'r'.

Reorder the terms:
-87 + -9 + -14r + 7r2 = 9 + -9

Combine like terms: -87 + -9 = -96
-96 + -14r + 7r2 = 9 + -9

Combine like terms: 9 + -9 = 0
-96 + -14r + 7r2 = 0

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

Divide each side by '7'.
-13.71428571 + -2r + r2 = 0

Move the constant term to the right:

Add '13.71428571' to each side of the equation.
-13.71428571 + -2r + 13.71428571 + r2 = 0 + 13.71428571

Reorder the terms:
-13.71428571 + 13.71428571 + -2r + r2 = 0 + 13.71428571

Combine like terms: -13.71428571 + 13.71428571 = 0.00000000
0.00000000 + -2r + r2 = 0 + 13.71428571
-2r + r2 = 0 + 13.71428571

Combine like terms: 0 + 13.71428571 = 13.71428571
-2r + r2 = 13.71428571

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 = 13.71428571 + 1

Reorder the terms:
1 + -2r + r2 = 13.71428571 + 1

Combine like terms: 13.71428571 + 1 = 14.71428571
1 + -2r + r2 = 14.71428571

Factor a perfect square on the left side:
(r + -1)(r + -1) = 14.71428571

Calculate the square root of the right side: 3.835920451

Break this problem into two subproblems by setting 
(r + -1) equal to 3.835920451 and -3.835920451.

Subproblem 1

r + -1 = 3.835920451 Simplifying r + -1 = 3.835920451 Reorder the terms: -1 + r = 3.835920451 Solving -1 + r = 3.835920451 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 = 3.835920451 + 1 Combine like terms: -1 + 1 = 0 0 + r = 3.835920451 + 1 r = 3.835920451 + 1 Combine like terms: 3.835920451 + 1 = 4.835920451 r = 4.835920451 Simplifying r = 4.835920451

Subproblem 2

r + -1 = -3.835920451 Simplifying r + -1 = -3.835920451 Reorder the terms: -1 + r = -3.835920451 Solving -1 + r = -3.835920451 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 = -3.835920451 + 1 Combine like terms: -1 + 1 = 0 0 + r = -3.835920451 + 1 r = -3.835920451 + 1 Combine like terms: -3.835920451 + 1 = -2.835920451 r = -2.835920451 Simplifying r = -2.835920451

Solution

The solution to the problem is based on the solutions from the subproblems. r = {4.835920451, -2.835920451}

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