Why is the answer not -140 as the value of a is 5 and b is -28. Also referring to the question in the same module where similar question were asked (eg- find value of a+b ), the signs of the values were taken into consideration

GRE GRE Quant Problem Solving
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Plugging in a = 5 and b = -28 yields (x + 5)^2 - (-28) = (x + 5)^2 + 28. Does that match with x^2 + 10x - 3?