If is a root of the equation , and is a root of the equation , where and are integers,
then the value of is
If is a root of the equation , and is a root of the equation , where and are integers,
then the value of is
Solution
When a quadratic equation with integer coefficients has an irrational root containing a square root, the conjugate of that root must also be a root.
If we have as a root where are rational and is not a perfect square, then must also be a root. This ensures that when we expand the quadratic, all coefficients remain integers since the irrational parts cancel out.
For the first equation:
Given root:
Missing root: (conjugate)
For the second equation:
Given root:
Missing root: (conjugate)
First equation with roots and :
Sum of roots:
Product of roots:
Using the identity :
Therefore:
Second equation with roots and :
Sum of roots:
Product of roots:
Therefore:
From :
, ,
From :
, ,
Substituting into :
Therefore:
Answer: D) 4
When we work with quadratic equations having integer coefficients and irrational roots, we should always remember that irrational roots come in conjugate pairs. This property allows us to quickly form the complete quadratic equation and find all coefficients.
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