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← JEE Main 2022 · 24 Jun · Shift 1
MathematicsInteger+4 / -1Question 25 of 90

JEE Main 2022 · 24 Jun · Shift 1, Mathematics question 25

The number of points where the function
f(x)={∣2x2−3x−7∣if x≤−1[4x2−1]if −1<x<1∣x+1∣+∣x−2∣if x≥1,f(x)=\begin{cases}|2x^2-3x-7| & \text{if } x\le-1\\ [4x^2-1] & \text{if } -1<x<1\\ |x+1|+|x-2| & \text{if } x\ge1,\end{cases}
[t][t] denotes the greatest integer ≤t\le t, is discontinuous is ______.

Answer and worked solution

Official answer: 7

Middle piece. On (−1,1)(-1,1), 4x2−14x^2-1 runs over [−1,3)[-1,3). The floor jumps where 4x2−1=0,1,24x^2-1=0,1,2: x=±12,±12,±32x=\pm\frac12,\pm\frac1{\sqrt2},\pm\frac{\sqrt3}2, six points. At x=0x=0 it is −1-1 on both sides (no jump).

At x=−1x=-1. f(−1)=∣2+3−7∣=2f(-1)=|2+3-7|=2 and the right limit is [3−]=2[3^-]=2: continuous.

At x=1x=1. Left limit 2, but f(1)=2+1=3f(1)=2+1=3: discontinuous.

Total 6+1=76+1=7.

Answer: 7