SOLUTION: If z=3 is a solution of the equation z^2 + kz + 15=0 then value of k is A)8 B)-8 C)-5 D)5

Question 1132298: If z=3 is a solution of the equation z^2 + kz + 15=0 then value of k is
A)8
B)-8
C)-5
D)5
Answer by ikleyn(52781) (Show Source): You can put this solution on YOUR website!
.

According to the Vieta's theorem, the product of the roots is equal to the value of the constant term of a polynomial.


Since the number 3 is the root and since the constant term is 15, then the second root is   = 5.


According to the Vieta's theorem, the sum of the roots is equal to the coefficient at x taken with the opposite sign.


Since the roots are 3 and 5, it implies that k = -(3+5) = -8.     ANSWER

Solved. The value of "k" is -8: Option B).

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