Find Two Consecutive Negative Integers Whose Product Is 90.?


2 Answers

Nishi Profile
Nishi answered
Two consecutive negative integers are-9 and -10-9 x -10 =90   as - x - =+
Oddman Profile
Oddman answered
-10, -9
thanked the writer.
Anonymous commented
Thank very much Oddman, what is now my doubt is the process (steps or formula) used to solve the problem. Would you please assist me on that?
Oddman commented
You can write an equation, such as n(n+1)=90, and solve for n, the lowest of the two integers. If you solve this by factoring, you are back where you started. The only way to avoid the problem of finding factors of 90 is to use the quadratic formula.
Oddman commented
Using the quadratic formula, you find the solutions are n = (-1±√(1^2+4*90))/2 = (-1±19)/2 = {-10, 9}. You are interested in the negative solution, n=-10, so n+1=-9.

90 isn't that hard to factor. An obvious factor is 10, leaving 9 as the other one. These have a difference of 1, so the only adjustment required is to make them both negative.

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