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If `a gt 0` and `lim_(xrarr oo) {sqrt(x^2+x+1)-(ax+b)}=0`, then `(a,b)` lies on the line.A. `x-y+3=0`B. `3x+4y-5=0`C. `x+6y+2=0`D. `x+2y+3=0`

Answer» Correct Answer - B
We have,
`lim_(xto oo) {sqrt(x^2+x+1)-(ax+b)}=0`
`lim_(xtooo)(x^2+x+1-(ax+b)^2)/(sqrt(x^2+x+1)ax+b)=0`
`rArrlim_(xtooo)(x^2(1-a^2)+x(1-2ab)+(1-b^2))/(sqrt(x^2+x+1)(ax+b))=0`
` rArr 1-a^2=0,1-2ab=0`
` rArr a=1 and b=(1)/(2)`
Clearly, `(a,b)=(1,(1)/(2))` lies on the line `3x+4y-5=0`.


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