Q.If x+1∣x+1∣>0,x∈R, then (A) x∈[−1,∞) (B) x∈(−1,∞) (C) x∈(−∞,−1) (D) x∈(−∞,−1]
Concept understanding — Linear and Modulus Inequalities
An inequality compares two expressions using <, ≤, > or ≥, and its solution is a range of values rather than a single number.
A linear inequality in one variable (e.g. 3x−5<7) is solved just like a linear equation, with one crucial rule: multiplying or dividing both sides by a negative number reverses the inequality sign. The answer is an interval such as x<4, i.e. (−∞,4). When the variable is restricted to a domain — natural numbers N, whole numbers, or integers Z — only the values of that type lying inside the range are solutions.
A modulus (absolute-value) inequality uses ∣x∣, the distance of x from 0. Two standard results convert it into ordinary linear inequalities (for a>0):
- ∣x∣<a⟺−a<x<a
- ∣x∣>a⟺x<−a or x>a
More generally ∣x−c∣<a⟺c−a<x<c+a (all points within distance a of c). Solve the resulting linear inequalities and combine the solution sets.
The quotient x+1∣x+1∣ equals +1 exactly when x+1 is positive and is undefined when x+1=0, so it is greater than zero only for x+1>0. That gives the open interval (−1,∞).
(B) x∈(−1,∞).
x+1∣x+1∣>0 holds precisely where x+1>0, i.e. x>−1, excluding x=−1 where it is undefined.
For t=0: t∣t∣={+1,−1,t>0t<0, with the expression undefined at t=0.
- Let t=x+1; the expression is t∣t∣.
- If t>0, ∣t∣=t, so t∣t∣=1>0. ✓
- If t<0, ∣t∣=−t, so t∣t∣=−1<0. ✗
- At t=0 the fraction is undefined, so x=−1 is excluded.
- Thus the inequality needs t>0⇒x+1>0⇒x>−1, giving x∈(−1,∞).
(B) x∈(−1,∞)
- CBSE 2025Set 465/S/WXYZ/41 markMCQQ.If x+1∣x+1∣>0,x∈R, then (A) x∈[−1,∞) (B) x∈(−1,∞) (C) x∈(−∞,−1) (D) x∈(−∞,−1]
›Reveal solutionSolution
x+1∣x+1∣>0 holds precisely where x+1>0, i.e. x>−1, excluding x=−1 where it is undefined.
For t=0: t∣t∣={+1,−1,t>0t<0, with the expression undefined at t=0.
- Let t=x+1; the expression is t∣t∣.
- If t>0, ∣t∣=t, so t∣t∣=1>0. ✓
- If t<0, ∣t∣=−t, so t∣t∣=−1<0. ✗
- At t=0 the fraction is undefined, so x=−1 is excluded.
- Thus the inequality needs t>0⇒x+1>0⇒x>−1, giving x∈(−1,∞).
✓Final answer(B) x∈(−1,∞)
- CBSE 2025Set 465/S/WXYZ/41 markMCQQ.Assertion (A) : Solution set of inequality ∣3x−2∣≤21, x∈R is [21,65]. Reason (R) : ∣x−a∣≤r⇔x≤a−r or x≥a+r. (A) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A). (B) Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of the Assertion (A). (C) Assertion (A) is true, but Reason (R) is false. (D) Assertion (A) is false, but Reason (R) is true.
›Reveal solutionSolution
The Assertion's solution set [21,65] is correct, but the Reason misstates the modulus rule (it describes ≥, not ≤), so (C).
Correct rule: ∣x−a∣≤r⟺a−r≤x≤a+r (a closed interval), whereas ∣x−a∣≥r⟺x≤a−r or x≥a+r.
- Solve the Assertion: ∣3x−2∣≤21⟺−21≤3x−2≤21.
- Add 2 throughout: 23≤3x≤25.
- Divide by 3: 21≤x≤65, i.e. solution set [21,65] — Assertion is true.
- Examine the Reason: it claims ∣x−a∣≤r⇔x≤a−r or x≥a+r. That "or" form is the rule for ∣x−a∣≥r, not ≤r. So the Reason is false.
- Assertion true, Reason false ⇒ option (C).
✓Final answer(C) Assertion (A) is true, but Reason (R) is false.
- CBSE 2024Set 465/RQPS/41 markMCQQ.If x>y and z<0, then : (A) xz>yz (B) xz≥yz (C) zx>zy (D) zx<zy
›Reveal solutionSolution
Dividing both sides of x>y by the negative number z reverses the inequality, so zx<zy.
If a>b and c<0, then ac<bc and ca<cb (multiplying/dividing by a negative reverses the inequality).
- Given x>y and z<0.
- Multiplying by z<0 reverses the sign: xz<yz — so options (A) and (B) are wrong.
- Dividing by z<0 also reverses the sign: zx<zy — so (C) is wrong and (D) is correct.
✓Final answer(D) zx<zy
- CBSE 2023Set 465/EF1GH/41 markMCQQ.If x+1∣x+1∣>0, x∈R, then :(a) x∈[−1,∞)(b) x∈(−1,∞)(c) x∈(−∞,−1)(d) x∈(−∞,−1]
›Reveal solutionSolution
x+1∣x+1∣>0 forces x+1>0, i.e. x∈(−1,∞).
For t=0: t∣t∣=+1 if t>0 and −1 if t<0; it is undefined at t=0.
- Let t=x+1. The expression t∣t∣>0 holds only when t>0.
- So x+1>0⇒x>−1.
- At x=−1 the expression is 00, undefined, so −1 is excluded — the endpoint is open.
- Hence the solution set is the open interval (−1,∞); option (a) wrongly includes −1.
✓Final answer(b) x∈(−1,∞)
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