Animated Solution for Mathematics - Quadratic Equations: Let S be the set of all real roots of the equation, 3x(3x−1)+2∣3x−1∣+∣3x−2∣=0. Then S:
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Visualized Solution
Substitution: 3x=t
Let 3x=t. Since 3x>0 for all real x, we have t>0.
The equation becomes: t(t−1)+2∣t−1∣+∣t−2∣=0.
Identifying Critical Points
The absolute value terms ∣t−1∣ and ∣t−2∣ change sign at t=1 and t=2.
These are our critical points.
We divide the domain t>0 into three intervals: (0,1), [1,2], and (2,∞).
Case 1: 0<t<1
Case 1:0<t<1
Both (t−1) and (t−2) are negative.
∣t−1∣=−(t−1)=1−t
∣t−2∣=−(t−2)=2−t
Solving Case 1
Substitute into equation: t(t−1)+2(1−t)+(2−t)=0
Expand: t2−t+2−2t+2−t=0
Simplify: t2−4t+4=0⇒(t−2)2=0
Root t=2 is not in (0,1). No solution here.
Case 2: 1≤t≤2
Case 2:1≤t≤2
Here, (t−1)≥0 but (t−2)≤0.
∣t−1∣=t−1
∣t−2∣=2−t
Solving Case 2
Substitute: t(t−1)+2(t−1)+(2−t)=0
Expand: t2−t+2t−2+2−t=0
Simplify: t2=0⇒t=0
Root t=0 is not in [1,2]. No solution here.
Case 3: t>2
Case 3:t>2
Both (t−1) and (t−2) are positive.
∣t−1∣=t−1
∣t−2∣=t−2
Solving Case 3
Substitute: t(t−1)+2(t−1)+(t−2)=0
Expand: t2−t+2t−2+t−2=0
Simplify: t2+2t−4=0
Quadratic formula: t=2−2±4−4(1)(−4)=−1±5
Rejecting Case 3
Positive root: t=5−1≈1.236
We assumed t>2.
Since 1.236>2, this root is also rejected.
All cases yielded no valid roots!
The Graphical Proof
Let f(t)=t(t−1)+2∣t−1∣+∣t−2∣
From the graph, the minimum value occurs at t=1.
f(1)=1(0)+2(0)+∣−1∣=1
Since f(t)≥1>0 for all t>0, f(t)=0 has no real roots.
The JEE Trap (Typo in Original Question)
The mathematically correct answer is 0 roots (Empty Set).
However, the official answer key states Singleton Set (1 root).
Why? The original exam had a typo. The intended equation was:
3x(3x−1)+2∣3x−1∣−∣3x−2∣=0
With the minus sign, t=5−1 becomes a valid root in Case 2!
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The Sigma Insight: Solution of Quadratic Equations
Solution Diagram
Analyzing the Setup
Welcome, fellow explorer of the mathematical landscape. Today, we are standing before a formidable-looking equation:
3x(3x−1)+2∣3x−1∣+∣3x−2∣=0
At first glance, it might seem like a chaotic mess of exponentials and absolute values. In the world of JEE Advanced, complexity is often just a mask for elegance. Let us peel back that mask together.
The Power of Substitution
The first thing that should catch your eye is the recurring presence of 3x. Whenever you see a repeated structure, think of it as a signal to simplify.
Let us define a new variable, t=3x. Because 3x is an exponential function, it is strictly positive for all real x. Therefore, our new variable must satisfy the constraint t>0.
With this substitution, our 'monster' equation transforms into a much friendlier polynomial form:
t(t−1)+2∣t−1∣+∣t−2∣=0
The Anatomy of the Modulus
Think of the modulus function as a mirror that flips negative values to positive. The expressions inside, t−1 and t−2, are the 'critical points' where the mirror flips.
Specifically, t−1 changes sign at t=1, and t−2 changes sign at t=2. These points divide our number line into three distinct territories: 0<t<1, 1≤t≤2, and t>2.
We must investigate each territory to see if any roots are hiding there.
The Three-Act Play
Act I: The Region (0,1)
In this region, both t−1 and t−2 are negative. The modulus bars force them to flip: ∣t−1∣=1−t and ∣t−2∣=2−t.
Substituting these into our equation:
t(t−1)+2(1−t)+(2−t)=0
Expanding this, we find t2−t+2−2t+2−t=0, which simplifies to t2−4t+4=0. This is a perfect square: (t−2)2=0, leading to t=2.
Since our condition for this act was t<1, this root is an imposter. We reject it.
Act II: The Region [1,2]
Here, t−1 is non-negative, but t−2 is negative. Thus, ∣t−1∣=t−1 and ∣t−2∣=2−t.
Our equation becomes:
t(t−1)+2(t−1)+(2−t)=0
Expanding this, we get t2−t+2t−2+2−t=0. The terms collapse beautifully, leaving us with t2=0, or t=0.
Since 0 is not in the range [1,2], we reject this root as well.
Act III: The Region t>2
In the land of t>2, both expressions are positive. The modulus bars vanish, leaving:
t(t−1)+2(t−1)+(t−2)=0
Expanding this, we get t2−t+2t−2+t−2=0, which simplifies to t2+2t−4=0. Using the quadratic formula:
t=2−2±4−4(1)(−4)=−1±5
Since t must be positive, we take t=5−1≈1.236. Because 1.236 is not greater than 2, we must reject this root.
The Conclusion
We have searched every region and found no valid roots. Graphically, this means the function f(t)=t(t−1)+2∣t−1∣+∣t−2∣ never touches the x-axis; it sits entirely above it.
The set of real roots is the empty set. Never doubt your math—it is the most reliable compass you have.