Find Quadratic Equation Given 1 Root: (2^(1/2)+1)

In summary, we were given the information that one root of a quadratic equation with rational coefficients is 2^(1/2)+1 and we needed to find the quadratic equation. Using the quadratic formula and the given root, we can determine that the other root is 1-(2^(1/2)) and the equation is x^2-2x-1=0.
  • #1
ritwik06
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Homework Statement



If one root of a quadratic equation with rational co-efficient is (2^(1/2)+1) , then find the quadratic equation.

Homework Equations



x=(-b+d^1/2)/2a
d=b^2-4ac


The Attempt at a Solution



Well, I can't quite understand this question. Please help me to understand what is given in the following statemnt.
 
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  • #2
If the only square root in the solution is [itex]\sqrt{2}[/itex], what must d be? Since the only difference between roots of a quadratic equation is that [itex]\pm[/itex] before the square root, what must the other root be?

Another, more "sophisticated" method:
Any quadratic, [itex]ax^2+ bx+ c[/itex] can be written [itex]a(x- x_0)(x- x_1)= ax^2- a(x_0+x_1)+ ax_0x_1[/itex] where [itex]x_0[/itex] and [itex]x_1[/itex] are roots of the equation. If one root is [itex]1+ \sqrt{2}[/itex] what must the other be so that both [itex]x_0+ x_1[/itex] and [itex]x_0x_1[/itex] are rational?
 
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  • #3
Well, Please check this. I think the othr root is 1-(2^1/2). thre fore the quadratic equation is x^2-2x-1=0
Am I right?
 
  • #4
Yes, that is correct.
 

FAQ: Find Quadratic Equation Given 1 Root: (2^(1/2)+1)

What is a quadratic equation?

A quadratic equation is a polynomial equation of the form ax^2 + bx + c = 0, where a, b, and c are constants and x is the variable. It is called quadratic because the highest power of x is 2.

How do you find the quadratic equation given one root?

To find the quadratic equation given one root, you can use the formula (x-r)(x-s) = 0, where r is the known root and s is the other root. In this case, the given root is (2^(1/2)+1), so the other root would be its conjugate (2^(1/2)-1). Plugging these values into the formula, we get (x-(2^(1/2)+1))(x-(2^(1/2)-1)) = 0, which simplifies to x^2 - 2^(1/2)x + 1 = 0. Therefore, the quadratic equation is x^2 - 2^(1/2)x + 1 = 0.

What is the significance of having a root in the form (2^(1/2)+1)?

Having a root in the form (2^(1/2)+1) means that the root is irrational, which implies that the quadratic equation has no rational roots. This also means that the graph of the equation will not intersect the x-axis at any rational point.

How can I graph the quadratic equation given one root?

To graph the quadratic equation given one root, you can plot the known root on the x-axis and use the symmetry property of quadratic functions to plot the other root. Then, you can plot a few additional points by plugging in different values for x and use the shape of the graph to plot the rest of the points.

Can a quadratic equation have more than one root?

Yes, a quadratic equation can have two distinct roots, one repeated root, or no real roots. This depends on the discriminant (b^2-4ac) of the equation. If the discriminant is positive, the equation will have two distinct roots. If it is zero, the equation will have one repeated root. If it is negative, the equation will have no real roots.

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