r^2-3r=40

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Solution for r^2-3r=40 equation:


Simplifying
r2 + -3r = 40

Reorder the terms:
-3r + r2 = 40

Solving
-3r + r2 = 40

Solving for variable 'r'.

Reorder the terms:
-40 + -3r + r2 = 40 + -40

Combine like terms: 40 + -40 = 0
-40 + -3r + r2 = 0

Factor a trinomial.
(-5 + -1r)(8 + -1r) = 0

Subproblem 1

Set the factor '(-5 + -1r)' equal to zero and attempt to solve: Simplifying -5 + -1r = 0 Solving -5 + -1r = 0 Move all terms containing r to the left, all other terms to the right. Add '5' to each side of the equation. -5 + 5 + -1r = 0 + 5 Combine like terms: -5 + 5 = 0 0 + -1r = 0 + 5 -1r = 0 + 5 Combine like terms: 0 + 5 = 5 -1r = 5 Divide each side by '-1'. r = -5 Simplifying r = -5

Subproblem 2

Set the factor '(8 + -1r)' equal to zero and attempt to solve: Simplifying 8 + -1r = 0 Solving 8 + -1r = 0 Move all terms containing r to the left, all other terms to the right. Add '-8' to each side of the equation. 8 + -8 + -1r = 0 + -8 Combine like terms: 8 + -8 = 0 0 + -1r = 0 + -8 -1r = 0 + -8 Combine like terms: 0 + -8 = -8 -1r = -8 Divide each side by '-1'. r = 8 Simplifying r = 8

Solution

r = {-5, 8}

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