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Question 252885: If m^2 = 17 then what is the value of (m - 1)(m + 1) ?
(A) √17 - 1 (B) √17 + 1 (C) 16 (D) 18 (E) 288
Answer by Theo(13342)   (Show Source):
You can put this solution on YOUR website! m^2 = 17 means that m = +/- sqrt(17)
(m-1)*(m+1) becomes:
(sqrt(17)-1)*(sqrt(17)+1
or:
(-sqrt(17) - 1) * (-sqrt(17) + 1)
if (sqrt(17)-1)*(sqrt(17)+1, then the product of these 2 factors is processed as follows:
sqrt(17) * sqrt(17) = 17
sqrt(17) * 1 = sqrt(17)
-1 * sqrt(17) = -sqrt(17)
-1 * 1 = -1
add these together to get 17 + sqrt(17) - sqrt(17) - 1 = 17 - 1 = 16
if (-sqrt(17)-1)*(-sqrt(17)+1, then the product of these 2 factors is processed as follows:
-sqrt(17) * -sqrt(17) = 17
-sqrt(17) * 1 = -sqrt(17)
-1 * -sqrt(17) = sqrt(17)
-1 * 1 = -1
add these together to get 17 - sqrt(17) + sqrt(17) - 1 = 17 - 1 = 16
answer would be selection C (16).
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