Rewrite 2x^2+x=15 as 2x^2+ x - 15 = 0. Use your favorite method to solve this for x. I prefer synthetic div., so will check out whether or not 2 is a root:
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2 / 2 1 -15
4 10
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2 5 -5 Since there is a non-zero remainder, 2 is NOT a root. Eliminate the 3rd answer choice.
Try -3. If used as a divisor in synth. div., will the remainder be zero or not zero? If zero, then -3 is a solution / root.
And so on.
