2r^2=r+21

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Solution for 2r^2=r+21 equation:


Simplifying
2r2 = r + 21

Reorder the terms:
2r2 = 21 + r

Solving
2r2 = 21 + r

Solving for variable 'r'.

Reorder the terms:
-21 + -1r + 2r2 = 21 + r + -21 + -1r

Reorder the terms:
-21 + -1r + 2r2 = 21 + -21 + r + -1r

Combine like terms: 21 + -21 = 0
-21 + -1r + 2r2 = 0 + r + -1r
-21 + -1r + 2r2 = r + -1r

Combine like terms: r + -1r = 0
-21 + -1r + 2r2 = 0

Factor a trinomial.
(-3 + -1r)(7 + -2r) = 0

Subproblem 1

Set the factor '(-3 + -1r)' equal to zero and attempt to solve: Simplifying -3 + -1r = 0 Solving -3 + -1r = 0 Move all terms containing r to the left, all other terms to the right. Add '3' to each side of the equation. -3 + 3 + -1r = 0 + 3 Combine like terms: -3 + 3 = 0 0 + -1r = 0 + 3 -1r = 0 + 3 Combine like terms: 0 + 3 = 3 -1r = 3 Divide each side by '-1'. r = -3 Simplifying r = -3

Subproblem 2

Set the factor '(7 + -2r)' equal to zero and attempt to solve: Simplifying 7 + -2r = 0 Solving 7 + -2r = 0 Move all terms containing r to the left, all other terms to the right. Add '-7' to each side of the equation. 7 + -7 + -2r = 0 + -7 Combine like terms: 7 + -7 = 0 0 + -2r = 0 + -7 -2r = 0 + -7 Combine like terms: 0 + -7 = -7 -2r = -7 Divide each side by '-2'. r = 3.5 Simplifying r = 3.5

Solution

r = {-3, 3.5}

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