
(5) Find a quadratic equation with integer coefficients having the following roots:
9SOLUTION:5
-------- 16
Let p(x) be the required quadratic with integer coefficients.
Since each of the two roots gives a linear factor of p(x), we have
p(x) = K[x - (9+5
)/16][x - (9-5
)/16]
= (K/256)[16x - (9+5
)][16x - (9-5
)]
= (K/256)[256x2 - 288x - 744]
So K can be any nonzero number such that K/256 is an integer and p(x) will
have integer coefficients. By construction, the original two numbers are
roots of p(x). If K = 256, we get the quadratic equation
256x2 - 288x - 744 = 0 (*)
We can make the coefficients even smaller integers by noting that each
coefficient in (*) is divisible by 8, which gives the equation:
32x2 - 36x - 93 = 0.