SOLUTION: If one root of the equation ... 2x^2+10x+k=0 is -2, find K and the other root?

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Question 390071: If one root of the equation ... 2x^2+10x+k=0 is -2, find K and the other root?
Found 2 solutions by robertb, ewatrrr:
Answer by robertb(5830) About Me  (Show Source):
You can put this solution on YOUR website!
Put x = -2 into the equation: 2%2A%28-2%29%5E2+%2B+10%2A-2+%2B+k+=+0 ====> 8 - 20 + k = 0, or -12 + k = 0, or k = 12. The equation is then 2x%5E2+%2B+10x+%2B+12+=+0. The equation simplifies to x%5E2+%2B+5x+%2B+6+=+0, which is the same as (x + 2)(x+3)= 0, so the other root is -3.

Answer by ewatrrr(24785) About Me  (Show Source):
You can put this solution on YOUR website!


Hi,        

2x^2+10x+k=0 when x = -2

 2(-2)^2 + 10*(-2) + k = 0

    8 - 20 + k = 0

            k = 12



2x^2+10x+12=0

2(x^2 + 5x + 6) = 0

(x^2 + 5x + 6) = 0

factoring

( x+2)(x+ 3)= 0 Note:SUM of the inner product(2x) and the outer product(3x) = 5x

( x+2)= 0

    x = -2  Already determined

(x+ 3)= 0

    x = -3, the other root