How would you solve 185r-80r^3=105? With steps please?

185r - 80r^3 = 105 The rule is you can do any valid operation on both sides of an equation and it will still be equal. Subtract 105.

185r - 80r^3 - 105 = 0 Rewrite.

-80r^3 + 185r - 105 = 0 Multiply by -1.

80r^3 - 185r + 105 = 0 This is called standard form: all variables on the left side in order of their powers, no fractions, and 0 or a constant on the right side. We can reduce this some more by dividing by 5.

16r^3 - 37r + 21 = 0

Now study this page until it seems obvious: en.wikipedia.org/wiki/Polynomial_remainder_theorem

So we are looking for something of the form (ar + b)(cr + d)(er + f) = 0.

http://www.wolframalpha.com/input/?i=16r^3+-+37r+%2B+21+%3D+0