Question

The discriminant if a quadratic equation is negative. One solution is 4 + 7i. What is the other solution? *

Answer 1

Answer:  B) 4 - 7i

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Explanation:

When you have a quadratic in the form ax^2 + bx + c = 0, where a,b,c are real numbers, then a negative discriminant leads to having a pair of complex roots. The roots come in conjugate pairs meaning that p+qi is one root while p-qi is the other root. The p,q are real numbers.

In the case of 4+7i being one root, we have p = 4 and q = 7, since it matches with p+qi. The other root must be 4-7i since it matches with p-qi.

In short, we flip the plus to a minus when going from 4+7i to 4-7i. All of this applies when we have a,b,c as real numbers.

If we allowed a,b,c to be complex numbers, then the roots may not necessarily come in conjugate pairs.