25-r^2=4r

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Solution for 25-r^2=4r equation:


Simplifying
25 + -1r2 = 4r

Solving
25 + -1r2 = 4r

Solving for variable 'r'.

Reorder the terms:
25 + -4r + -1r2 = 4r + -4r

Combine like terms: 4r + -4r = 0
25 + -4r + -1r2 = 0

Begin completing the square.  Divide all terms by
-1 the coefficient of the squared term: 

Divide each side by '-1'.
-25 + 4r + r2 = 0

Move the constant term to the right:

Add '25' to each side of the equation.
-25 + 4r + 25 + r2 = 0 + 25

Reorder the terms:
-25 + 25 + 4r + r2 = 0 + 25

Combine like terms: -25 + 25 = 0
0 + 4r + r2 = 0 + 25
4r + r2 = 0 + 25

Combine like terms: 0 + 25 = 25
4r + r2 = 25

The r term is 4r.  Take half its coefficient (2).
Square it (4) and add it to both sides.

Add '4' to each side of the equation.
4r + 4 + r2 = 25 + 4

Reorder the terms:
4 + 4r + r2 = 25 + 4

Combine like terms: 25 + 4 = 29
4 + 4r + r2 = 29

Factor a perfect square on the left side:
(r + 2)(r + 2) = 29

Calculate the square root of the right side: 5.385164807

Break this problem into two subproblems by setting 
(r + 2) equal to 5.385164807 and -5.385164807.

Subproblem 1

r + 2 = 5.385164807 Simplifying r + 2 = 5.385164807 Reorder the terms: 2 + r = 5.385164807 Solving 2 + r = 5.385164807 Solving for variable 'r'. Move all terms containing r to the left, all other terms to the right. Add '-2' to each side of the equation. 2 + -2 + r = 5.385164807 + -2 Combine like terms: 2 + -2 = 0 0 + r = 5.385164807 + -2 r = 5.385164807 + -2 Combine like terms: 5.385164807 + -2 = 3.385164807 r = 3.385164807 Simplifying r = 3.385164807

Subproblem 2

r + 2 = -5.385164807 Simplifying r + 2 = -5.385164807 Reorder the terms: 2 + r = -5.385164807 Solving 2 + r = -5.385164807 Solving for variable 'r'. Move all terms containing r to the left, all other terms to the right. Add '-2' to each side of the equation. 2 + -2 + r = -5.385164807 + -2 Combine like terms: 2 + -2 = 0 0 + r = -5.385164807 + -2 r = -5.385164807 + -2 Combine like terms: -5.385164807 + -2 = -7.385164807 r = -7.385164807 Simplifying r = -7.385164807

Solution

The solution to the problem is based on the solutions from the subproblems. r = {3.385164807, -7.385164807}

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