The problem asks us to find the values of $k$ for which the quadratic equation $x^2 - kx + 3 - k = 0$ has real roots.

AlgebraQuadratic EquationsDiscriminantInequalitiesReal Roots
2025/4/5

1. Problem Description

The problem asks us to find the values of kk for which the quadratic equation x2kx+3k=0x^2 - kx + 3 - k = 0 has real roots.

2. Solution Steps

For a quadratic equation ax2+bx+c=0ax^2 + bx + c = 0 to have real roots, the discriminant must be greater than or equal to zero. The discriminant is given by the formula:
D=b24acD = b^2 - 4ac
In our equation, x2kx+3k=0x^2 - kx + 3 - k = 0, we have a=1a = 1, b=kb = -k, and c=3kc = 3 - k. So, we need to find the values of kk for which:
D=(k)24(1)(3k)0D = (-k)^2 - 4(1)(3 - k) \ge 0
k24(3k)0k^2 - 4(3 - k) \ge 0
k212+4k0k^2 - 12 + 4k \ge 0
k2+4k120k^2 + 4k - 12 \ge 0
Now we need to factor the quadratic expression k2+4k12k^2 + 4k - 12. We are looking for two numbers that multiply to 12-12 and add up to 44. Those numbers are 66 and 2-2.
So, we can factor the expression as:
(k+6)(k2)0(k + 6)(k - 2) \ge 0
Now we analyze the inequality (k+6)(k2)0(k + 6)(k - 2) \ge 0. The critical points are k=6k = -6 and k=2k = 2. We test the intervals:
* k<6k < -6: Choose k=7k = -7. Then (7+6)(72)=(1)(9)=9>0(-7 + 6)(-7 - 2) = (-1)(-9) = 9 > 0. So, k<6k < -6 is part of the solution.
* 6<k<2-6 < k < 2: Choose k=0k = 0. Then (0+6)(02)=(6)(2)=12<0(0 + 6)(0 - 2) = (6)(-2) = -12 < 0. So, 6<k<2-6 < k < 2 is not part of the solution.
* k>2k > 2: Choose k=3k = 3. Then (3+6)(32)=(9)(1)=9>0(3 + 6)(3 - 2) = (9)(1) = 9 > 0. So, k>2k > 2 is part of the solution.
Since we have 0\ge 0, we include the critical points k=6k = -6 and k=2k = 2. Therefore, the solution is k6k \le -6 or k2k \ge 2.

3. Final Answer

k6k \le -6 or k2k \ge 2

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