the rational root theorem the rational root theorem gives us a tool to predict the values of...
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The Rational Root Theorem
The Rational Root Theorem gives us a tool to predict the Values of Rational Roots:
If P(x) a0 xn a1 xn 1 ... an 1x an , where the
coeffiecients are all integers,
& a rational zero of P(x) in reduced form is p
q, then
p must be a factor of an (the constant term) &
q must be a factor of a0 (the leading coefficient).
List the Possible Rational Roots
For the polynomial: f (x) x3 3x2 5x 15
All possible values of: p: 1, 3, 5
q: 1
All possible Rational Roots of the form p/q:
p
q: 1, 3, 5
Find a Root That Works
For the polynomial:
Substitute each of our possible rational roots into f(x). If a value, a, is a root, then f(a) = 0. (Roots are solutions to an equation set equal to zero!)
f (1) 1 3 5 15 12
f (3) 27 27 15 15 0 *
f (5) 125 75 25 15 60
f (x) x3 3x2 5x 15
Find the Other Roots
x 3 x 3 3x2 5x 15
Find the Other Roots (con’t)
x 3 x 3 3x2 5x 15x2 5
The resulting polynomial is a quadratic, but it doesn’t have real factors. Solve the quadratic set equal to zero by either using the quadratic formula, or by isolating the x and taking the square root of both sides.
Find the Other Roots (con’t)
The solutions to the quadratic equation: x i 5, i 5
The three complex roots of the polynomial are: x 3, i 5, i 5
For the polynomial: f (x) x3 3x2 5x 15
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