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Algebra Difficulty 4.8 AIME Prove it Croatia

Determine all values of the real parameter mm for which the equation
(m1)x22mx+2=0 (m - 1)x^2 - 2mx + 2 = 0
has no real solutions.

Solution

Let us consider the quadratic equation:
(m1)x22mx+2=0. (m - 1)x^2 - 2mx + 2 = 0.
This equation has no real solutions if and only if its discriminant is negative.

The discriminant DD is:
D=[2m]24(m1)2=4m28(m1)=4m28m+8. D = [-2m]^2 - 4(m-1) \cdot 2 = 4m^2 - 8(m-1) = 4m^2 - 8m + 8.
We require:
4m28m+8<0. 4m^2 - 8m + 8 < 0.
Divide both sides by 44:
m22m+2<0. m^2 - 2m + 2 < 0.
But the quadratic m22m+2m^2 - 2m + 2 has discriminant:
(2)2412=48=4<0. (-2)^2 - 4 \cdot 1 \cdot 2 = 4 - 8 = -4 < 0.
So m22m+2m^2 - 2m + 2 is always positive for all real mm.

Therefore, there is **no real value of mm** for which the equation has no real solutions.

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