lim (√( x)-2)/(√ (x+5)-3)
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lim(x→4)(√( x)-2)/(√ (x+5)-3) (分子、分母分别有理化)
=lim(x→4)(√( x)-2)(√x+2)(√ (x+5)+3)/[(√ (x+5)-3) (√x+2)(√ (x+5)+3)]
=lim(x→4)(x-4)(√ (x+5)+3)/[(x-4)(√x+2)]
=lim(x→4)(√ (x+5)+3)/[(√x+2)]
=6/4
=3/2
=lim(x→4)(√( x)-2)(√x+2)(√ (x+5)+3)/[(√ (x+5)-3) (√x+2)(√ (x+5)+3)]
=lim(x→4)(x-4)(√ (x+5)+3)/[(x-4)(√x+2)]
=lim(x→4)(√ (x+5)+3)/[(√x+2)]
=6/4
=3/2
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