15. One of the roots of the equation x3 – 7x2 + 25x – 39 = 0 is 3. What are the other 2 roots of this equation?
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A. –1 and 5 |
B. –1 and 13 |
C. 2–(17)1/2 and 2+(17)1/2 |
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D. 2 – 3i and 2 + 3i |
E. 3 – 2i and 3 + 2i |
Solution: The answer is D
Since 3 is a root, then (x-3) is a factor of x3 – 7x2 + 25x – 39. Use the method of long division to find another factor, as follows:
Since x2 – 4x + 13 is not factorable, use the quadratic formula to find the other two roots.
