Algebra · real student question

Solve the equation -1/m + 1 - m = 0.

Question

Solve

1m+1m=0-\frac{1}{m}+1-m=0

Step-by-step solution

  1. Record the domain. The term 1m\tfrac1m forces m0m\neq 0, so any candidate root of 00 would have to be discarded.

  2. Multiply through by mm. Since m0m\neq 0 this is reversible:

    1+mm2=0-1+m-m^2=0

  3. Normalise the leading coefficient. Multiply by 1-1 so the m2m^2 term is positive:

    m2m+1=0m^2-m+1=0

  4. Compute the discriminant and read off the conclusion. With a=1a=1, b=1b=-1, c=1c=1:

    Δ=(1)24(1)(1)=14=3<0\Delta=(-1)^2-4(1)(1)=1-4=-3<0

    A negative discriminant means no real solutions. Geometrically, y=m2m+1=(m12)2+34y=m^2-m+1=\left(m-\tfrac12\right)^2+\tfrac34 has minimum value 34>0\tfrac34>0, so its graph never touches the axis.

  5. Give the complex roots for completeness. 3=i3\sqrt{-3}=i\sqrt3, so

    m=1±i32m=\frac{1\pm i\sqrt3}{2}

    These are the two primitive sixth roots of unity; each has modulus 11. Check: their sum is 11 and their product is 1+34=1\tfrac{1+3}{4}=1, matching ba-\tfrac{b}{a} and ca\tfrac{c}{a} \checkmark.

Answer

No real solution;m=1±i32 over C\text{No real solution};\quad m=\frac{1\pm i\sqrt{3}}{2}\ \text{over }\mathbb{C}

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