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where ? and ?? are yet to be determined. If I had values for ? and ?? I could expand the right side to verify that the factorization is correct. Expanding the right side gives me x^{2}, two x terms and a constant ? × ?? which must be 15. Thus ? and ?? must have opposite signs. Since 15 can only be factored as 1 × 15 or 3 × 5 the possible factorizations of x^{2} + 2x  15 are
Expand each of the possibilities to see if there is one that gives the x term as + 2x. Penny  


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