Theory of Intelligence
11TH•Mathematics•Theory Of Quadratic Functions•Question 4

Step-by-Step Solution

Solve the following absolute value quadratic equations and inequalities:

Step-by-Step Solution

Step 1: Check the Right-Hand Side

For any real solution to exist, the right-hand side must satisfy x2−x+1≥0x^2 - x + 1 \ge 0. Notice that:

x2−x+1=(x−12)2+34≥34>0(∀x∈R)x^2 - x + 1 = \left(x - \frac{1}{2}\right)^2 + \frac{3}{4} \ge \frac{3}{4} > 0 \quad (\forall x \in \mathbb{R})

Since the RHS is strictly positive for all real xx, no potential real solution will be rejected due to a negative RHS.

Step 2: Split into Two Cases

An equation ∣A∣=B|A| = B splits into:

A=BorA=−BA = B \quad \text{or} \quad A = -B

Step 3: Solve Case 1 (A=BA = B)

3x2−7x+2=x2−x+12x2−6x+1=0\begin{aligned} 3x^2 - 7x + 2 &= x^2 - x + 1 \\ 2x^2 - 6x + 1 &= 0 \end{aligned}

Using the quadratic formula:

x=−(−6)±(−6)2−4(2)(1)2(2)=6±36−84=6±284=6±274=3±72x = \frac{-(-6) \pm\sqrt{(-6)^2 - 4(2)(1)}}{2(2)} = \frac{6 \pm\sqrt{36 - 8}}{4} = \frac{6 \pm\sqrt{28}}{4} = \frac{6 \pm 2\sqrt{7}}{4} = \frac{3 \pm\sqrt{7}}{2}

Numerically: x≈3−2.6462≈0.177x \approx \frac{3 - 2.646}{2} \approx 0.177 and x≈3+2.6462≈2.823x \approx \frac{3 + 2.646}{2} \approx 2.823.

Step 4: Solve Case 2 (A=−BA = -B)

3x2−7x+2=−(x2−x+1)3x2−7x+2=−x2+x−14x2−8x+3=0\begin{aligned} 3x^2 - 7x + 2 &= -(x^2 - x + 1) \\ 3x^2 - 7x + 2 &= -x^2 + x - 1 \\ 4x^2 - 8x + 3 &= 0 \end{aligned}

Factor the quadratic trinomial:

(2x−1)(2x−3)=0x=12=0.5orx=32=1.5\begin{aligned} (2x - 1)(2x - 3) &= 0 \\ x = \frac{1}{2} = 0.5 \quad &\text{or} \quad x = \frac{3}{2} = 1.5 \end{aligned}

Step 5: Consolidate All Valid Solutions

All four solutions are real and yield valid equality:

x∈{12,  32,  3−72,  3+72}x \in \left\{ \frac{1}{2}, \; \frac{3}{2}, \; \frac{3 - \sqrt{7}}{2}, \; \frac{3 + \sqrt{7}}{2} \right\}

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