Given that
lim x → c f ( x ) = 3 4 \lim_{x\rightarrow c}f(x)=\frac{3}{4} lim x → c f ( x ) = 4 3
lim x → c g ( x ) = 12 \lim_{x\rightarrow c}g(x)=12 lim x → c g ( x ) = 12
lim x → c h ( x ) = − 3 \lim_{x\rightarrow c}h(x)=-3 lim x → c h ( x ) = − 3
We can use these values in the following examples to understand some of the limit theorems.
limit theorems.
Ex 1. lim x → c f ( x ) ± lim x → c g ( x ) \lim_{x\rightarrow c}f(x)\pm\lim_{x\rightarrow c}g(x) lim x → c f ( x ) ± lim x → c g ( x )
To find lim x → c f ( x ) ± lim x → c g ( x ) \lim_{x\rightarrow c}f(x)\pm\lim_{x\rightarrow c}g(x) lim x → c f ( x ) ± lim x → c g ( x ) , we use the given values,
lim x → c f ( x ) = 3 4 \lim_{x\rightarrow c}f(x)=\frac{3}{4} lim x → c f ( x ) = 4 3 and lim x → c g ( x ) = 12 \lim_{x\rightarrow c}g(x)=12 lim x → c g ( x ) = 12
Therefore,
= 3 4 ± ( 12 ) =\frac{3}{4}\pm(12) = 4 3 ± ( 12 )
= 3 4 + ( 12 ) = 51 4 =\frac{3}{4}+(12)=\frac{51}{4} = 4 3 + ( 12 ) = 4 51 and = 3 4 − ( 12 ) = − 45 4 =\frac{3}{4}-(12)=\frac{-45}{4} = 4 3 − ( 12 ) = 4 − 45
Ex 2. lim x → c [ ( 2. f ( x ) ) + 12. g ( x ) ] \lim_{x\rightarrow c}[(2.f(x))+\sqrt{12.g(x)}] lim x → c [( 2. f ( x )) + 12. g ( x ) ]
To find lim x → c [ ( 2. f ( x ) ) + 12. g ( x ) ] \lim_{x\rightarrow c}[(2.f(x))+\sqrt{12.g(x)}] lim x → c [( 2. f ( x )) + 12. g ( x ) ] , we use the given values,
lim x → c [ ( 2. f ( x ) ) + 12. g ( x ) ] = [ ( 2. lim x → c f ( x ) ) + 12. lim x → c g ( x ) ] \lim_{x\rightarrow c}[(2.f(x))+\sqrt{12.g(x)}]\\=[(2.\lim_{x\rightarrow c}f(x))+\sqrt{12.\lim_{x\rightarrow c}g(x)}] lim x → c [( 2. f ( x )) + 12. g ( x ) ] = [( 2. lim x → c f ( x )) + 12. lim x → c g ( x ) ]
= [ ( 2. 4 3 ) + ( 12 ) ( 12 ) ] =[(2.\frac{4}{3})+\sqrt{(12)(12)}] = [( 2. 3 4 ) + ( 12 ) ( 12 ) ]
= 8 3 + 12 = 44 3 =\frac{8}{3}+12=\frac{44}{3} = 3 8 + 12 = 3 44
lim x → c f ( x ) = 3 4 \lim_{x\rightarrow c}f(x)=\frac{3}{4} lim x → c f ( x ) = 4 3 and lim x → c g ( x ) = 12 \lim_{x\rightarrow c}g(x)=12 lim x → c g ( x ) = 12
Therefore,
= 2 ( 3 4 ) + ( 12 ) = 27 2 =2(\frac{3}{4})+(12)=\frac{27}{2} = 2 ( 4 3 ) + ( 12 ) = 2 27
Ex 3. l i m x → c 4 f ( x ) − g ( x ) 2 h ( x ) lim_{x\rightarrow c}4\frac{f(x)-g(x)}{2h(x)} l i m x → c 4 2 h ( x ) f ( x ) − g ( x )
= lim x → c 4 f ( x ) − lim x → c g ( x ) lim x → c 2 h ( x ) =\frac{\lim_{x\rightarrow c}4f(x)-\lim_{x\rightarrow c}g(x)}{\lim_{x\rightarrow c}2h(x)} = l i m x → c 2 h ( x ) l i m x → c 4 f ( x ) − l i m x → c g ( x )
= 4 lim x → c f ( x ) − lim x → c g ( x ) 2 lim x → c h ( x ) =\frac{4\lim_{x\rightarrow c}f(x)-\lim_{x\rightarrow c}g(x)}{2\lim_{x\rightarrow c}h(x)} = 2 l i m x → c h ( x ) 4 l i m x → c f ( x ) − l i m x → c g ( x )
= 4 ( 3 4 ) − ( 12 ) ( 2 ) ( − 3 ) =\frac{4(\frac{3}{4})-(12)}{(2)(-3)} = ( 2 ) ( − 3 ) 4 ( 4 3 ) − ( 12 )
= 3 2 =\frac{3}{2} = 2 3
Ex 4. l i m x → c [ h ( x ) − 4 f ( x ) ] lim_{x\rightarrow c}[h(x)-4f(x)] l i m x → c [ h ( x ) − 4 f ( x )]
= l i m x → c h ( x ) − 4 l i m x → c f ( x ) =lim_{x\rightarrow c}h(x)-4lim_{x\rightarrow c}f(x) = l i m x → c h ( x ) − 4 l i m x → c f ( x )
= ( − 3 ) − 4 ( 3 4 ) =(-3)-4(\frac{3}{4}) = ( − 3 ) − 4 ( 4 3 )
= − 3 − 3 =-3-3 = − 3 − 3
= − 6 =-6 = − 6
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