Question 1130135: Find two integers whose sum is -7 and whose product is 12.
Found 3 solutions by ikleyn, ankor@dixie-net.com, greenestamps:
Answer by ikleyn(52781)   (Show Source):
You can put this solution on YOUR website! .
-3 and -4.
---------------
3 seconds to read the problem.
PLUS 3-4 seconds to understand what they want from you.
PLUS 3-4 seconds to get the answer (mentally).
----------------
The other tutor demonstrated you another approach, but when he makes his factoring,
he actually performs THE SAME TRIAL and ERROR guessing as I did mentally.
Answer by ankor@dixie-net.com(22740)  (Show Source):
You can put this solution on YOUR website! Find two integers whose sum is -7
a + b = -7
b = -a - 7
and whose product is 12.
ab = 12
replace b with (-a - 7)
a(-a-7) = 12
arrange as quadratic equation
-a^2 - 7a - 12 = 0
multiply equation by -1, get rid of all those negatives
a^2 + 7a + 12 = 0
Factors to
(a+3)(a+4) = 0
a = -3, then b = -4
or
a = -4, then b = -3
Answer by greenestamps(13200)  (Show Source):
You can put this solution on YOUR website!
Solve mentally in a few second using logical reasoning.
(1) The product is positive, so the two integers must have the same sign.
(2) The sum is negative, so the two integers must both be negative.
So ignore the signs for the moment, and find two (positive) integers whose sum is 7 and whose product is 12. Then apply the negative signs to those two integers.
|
|
|
