Which expression is equivalent to x² - 4x - 45? А
(x - 9)(x - 5)
B
(x + 9)(x+5)
(20 +9)(x - 5)
D
(x - 9)(x+5)

D. (x - 9)(x+5)

Step-by-step explanation:

is your expression, so you have to factor it out. Since from the options available it's clear that the factors of -45 you use are some form of 9 and 5, we can use the process of elimination to figure out which are the correct ones.

First, through FOIL u know that in any factored form the last two terms in each bracket multiply together to make the last term in the expanded form.

So first, look at A. the last two terms are -9 and -5, which = 45 when multiplied together. 45 does not = -45, so it can't be A.

B has 9 and 5. When they're multiplied, they = 45, which does not = -45, so its not B

It can't be C either, because the first term of the first bracket in C is 20, and when multiplied with x it doesn't produce x^2.

Therefore it has to be D. u can check this by multiplying -9 and 5, which = -45, the final term in the expanded form. Also, -9 + 5 = -4, which is the middle term of the expanded form.

step-by-step explanation: a reaction is first order. if the initial reactant concentration is 0.0200 m, and 25.0 days later the concentration is 6.25 x 10-4 m, then its half-life is: