If x^2-2x-15=0 and x>0, which of the following must b equal to zero ?
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03 Jan 2024, 00:23
If \(x^2-2x-15=0\)
we can then obtain two factors \((x+3)\) and \((x-5)\). Since \(x>0\), should consider only the factor \((x-5)\).
Now, to find out which of the list of choices is equal to zero, we just have to simply find the expressions which can have at least \((x-5)\) as a factor.
Now only Choices B,C,E,F have constant terms that are multiples of \(5\), which I would expect when \((x-5)\) is a factor. But of these I will eliminate E and F, because the coefficient of the linear term is positive, when I would expect it to be negative, -7 for E, to obtain a constant term of 10, and -10 for F, to obtain a constant term of 25.
But Choices B and C offer me the very same coefficients for the linear term that I am looking for. Hence they are the correct choices.