MathematicsAlgebraic Operations on MatricesJEE Advanced 2008Moderate
Visualized Solution (Hindi)
Introduction to the Matching Problem
- Objective: Match Column I expressions with Column II values.
- Part A: Minimum value of f(x)=x+2x2+2x+4
- Part B: Matrix properties involving symmetry and commutativity.
- Part C: Logarithmic inequality for an integer k.
- Part D: General solution of a trigonometric equation.
Part A: Simplifying the Expression
- Rewrite f(x)=x+2x2+2x+4 by dividing the terms.
- f(x)=x+2(x+2)2+4−2(x+2) is not as clean as:
- f(x)=(x+2)+x+24−2
- Assume x+2>0 for a local minimum.
Part A: Applying AM-GM Inequality
- Apply AM-GM on (x+2) and x+24:
- 2(x+2)+x+24≥(x+2)⋅x+24
- (x+2)+x+24≥2⋅4=4
- Minimum value ymin=4−2=2
- Match: (A) → (r)
Part B: Matrix Commutativity
- Given: At=A (Symmetric) and Bt=−B (Skew-symmetric).
- Expand (A+B)(A−B)=(A−B)(A+B):
- A2−AB+BA−B2=A2+AB−BA−B2
- Simplify: 2BA=2AB⟹AB=BA
Part B: Finding the value of k
- Calculate (AB)t=BtAt=(−B)A=−BA
- Since AB=BA, then (AB)t=−AB
- Given (AB)t=(−1)kAB⟹(−1)k=−1
- Therefore, k must be an odd integer.
- Possible values for k: 1,3. Match: (B) → (q), (s)
Part C: Logarithmic Simplification
- Given a=log3log32⟹3a=log32
- Calculate 3−a=log321=log23
- Substitute into inequality: 1<2−k+log23<2
Part C: Solving for k
- Take log2 on all sides: 0<−k+log23<1
- Rearrange: log23−1<k<log23
- Since log23≈1.58, then 0.58<k<1.58
- The integer satisfying this is k=1.
- k=1 is less than 2 and 3. Match: (C) → (r), (s)
Part D: Trigonometric Equation
- Given sinθ=cosϕ⟹cos(2π−θ)=cosϕ
- General solution: 2π−θ=2nπ±ϕ
- Rearrange: θ±ϕ−2π=−2nπ
- Expression: π1(θ±ϕ−2π)=−2n (Even integers)
Part D: Final Matches
- Possible values are even integers: ...,−2,0,2,4,...
- From Column II, the values are 0 and 2.
- Match: (D) → (p), (r)
- Final Summary: A-r; B-q,s; C-r,s; D-p,r
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