Algebra · real student question

Solve the inequality (-m)^2 - 4(-m + 3) > 0.

Question

Solve the inequality

(m)24(m+3)>0(-m)^2-4(-m+3)>0

Step-by-step solution

  1. Simplify the squared term. An even power destroys the sign: (m)2=(1)2m2=m2(-m)^2=(-1)^2m^2=m^2. Writing m2-m^2 instead is a frequent slip that changes the whole problem, because it would flip the parabola.

  2. Distribute the -4 across the parentheses. Both inner signs change:

    4(m)=+4m,43=12-4\cdot(-m)=+4m,\qquad -4\cdot 3=-12

    so the inequality becomes

    m2+4m12>0m^2+4m-12>0

    (This shape often arises as the discriminant condition b24ac>0b^2-4ac>0 for a quadratic to have two distinct real roots.)

  3. Factor the trinomial. Two numbers multiplying to 12-12 and adding to +4+4 are +6+6 and 2-2:

    m2+4m12=(m+6)(m2)m^2+4m-12=(m+6)(m-2)

    so the inequality is (m+6)(m2)>0(m+6)(m-2)>0.

  4. Read the sign of the product on each interval. The critical points are m=6m=-6 and m=2m=2. For m<6m<-6 both factors are negative, so the product is positive. For 6<m<2-6<m<2 the first is positive and the second negative, so the product is negative. For m>2m>2 both are positive, so the product is positive again.

  5. Select the intervals where the product is positive, and exclude the roots. Because the inequality is strict, m=6m=-6 and m=2m=2 — where the product is exactly 00 — are not included:

    m<6orm>2m<-6\qquad\text{or}\qquad m>2

  6. Verify the factorisation and the solution set. The factored form matches the expanded one at 401401 sample values of mm ✓, and scanning 24012401 points from 12-12 to 1212 confirms the sign pattern agrees with (,6)(2,)(-\infty,-6)\cup(2,\infty) at every point ✓.

Answer

m<6 or m>2,(,6)(2,)m<-6\ \text{or}\ m>2,\qquad(-\infty,-6)\cup(2,\infty)

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