To determine if a function F(x) is continuous at a point x=c, three conditions must be met:
- F(c) must be defined.
- limx→cF(x) must exist.
- limx→cF(x)=F(c).
1. Determine whether the function F(x)=3x2+4x−10 is continuous at x=3 or not.
Step 1: Evaluate F(3).
F(3)=3(3)2+4(3)−10
F(3)=3(9)+12−10
F(3)=27+12−10
F(3)=39−10
F(3)=29
F(3) is defined.
Step 2: Evaluate limx→3F(x).
Since F(x) is a polynomial function, the limit as x approaches 3 can be found by direct substitution.
limx→3(3x2+4x−10)=3(3)2+4(3)−10
limx→3(3x2+4x−10)=27+12−10
limx→3(3x2+4x−10)=29
The limit exists.
Step 3: Compare F(3) and limx→3F(x).
Since F(3)=29 and limx→3F(x)=29, we have limx→3F(x)=F(3).
Therefore, the function F(x)=3x2+4x−10 is continuous at x=3.
Continuous
2. Is the function F(x)=2x+12x2+3 continuous at (i) x=−1 and (ii) x=−21?
A rational function is continuous everywhere except where its denominator is zero.
First, find the values of x for which the denominator is zero:
2x+1=0
2x=−1
x=−21
The function is undefined at x=−21.
a) Continuity at x=−1
Step 1: Evaluate F(−1).
F(−1)=2(−1)+12(−1)2+3
F(−1)=−2+12(1)+3
F(−1)=−12+3
F(−1)=−15
F(−1)=−5
F(−1) is defined.
Step 2: Evaluate limx→−1F(x).
Since x=−1 does not make the denominator zero, the limit can be found by direct substitution.
limx→−12x+12x2+3=2(−1)+12(−1)2+3
limx→−12x+12x2+3=−15
limx→−12x+12x2+3=−5
The limit exists.
Step 3: Compare F(−1) and limx→−1F(x).
Since F(−1)=−5 and limx→−1F(x)=−5, we have limx→−1F(x)=F(−1).
Therefore, the function F(x)=2x+12x2+3 is continuous at x=−1.
Continuousatx=−1
b) Continuity at x=−21
Step 1: Evaluate F(−21).
F(−21)=2(−21)+12(−21)2+3
F(−21)=−1+12(41)+3
F(−21)=021+3
F(−21)=027
Since the denominator is zero, F(−21) is undefined.
Because F(−21) is undefined, the first condition for continuity is not met.
Therefore, the function F(x)=2x+12x2+3 is discontinuous at x=−21.
Discontinuousatx=−21