2. For what value of b will f(x) = x2 + bx + 400 have -20 as its only zero?

The answer you are looking for is right in front of you it’s c. 3/20

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Look, when you want to do something like put it like x^2. x2 could mean x² or x₂. so to clear confusion, know the notation. to find the product multiply the x's and you get -8x and the y's and you get 6y. since it's all being multiplied it is just -8x6y, or answer a. although the better answer is -48xy(combining -8 and 6) because you should multiply constants whenever you can.