(5x^2-7x+23)+2x^2+9x-72)=7x^2-7x+9x+23-72=7x^2+2x+49
5 x ^ 2 + 2 x ^ 2 - 7 x + 9 x + 23 - 72 = 7 x ^ 2 + 2 x - 49
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