For the polynomial 6xy2−5x2y?+9x2 to be a trinomial with a degree of 3 after it has been fully simplified, what is the missing exponent of the y in the second term?

The first term, 6xy², has degree 1 + 2 = 3. For the second term, −5x²yⁿ, the degree is 2 + n, so setting it equal to 3 gives n = 1. Thus the missing exponent is 1, choice B.

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