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Consider two differentiable functions `f(x),g(x)` satisfying `6intf(x)g(x)dx=x^(6)+3x^(4)+3x^(2)+c and 2 int(g(x)dx)/(f(x))=x^(2)+c, " where " f(x) gt 0 AA x in R.` `lim_(x to 0) (log(f(x)))/(g(x))=`A. eB. 2C. 1D. 0 |
Answer» Correct Answer - D We have, `6intf(x)g(x)dx=x^(6)+3x^(4)+3x^(2)+c` Differentiating both sides w.r.t.x, we get `6f(x)g(x)=6x^(5)+12x^(3)+6x` ` :. f(x)g(x)=x^(5)+2x^(3)+x " ...(1)" ` `2 int (g(x)dx)/(f(x))=x^(2)+c` Differentiating both sides w.r.t.x, we get `(g(x))/(f(x))=x " ...(2)" ` Multiplying (1) and (2), we get `(g(x))^(2)=x^(6)+2x^(4)+x^(2)=(x^(3)+x)^(2)` ` :. g(x)=x^(3)+x` ` :. f(x)=x^(2)+1 " " ("as"f(x) gt 0).` Now ` int (g(x)-f(x))dx=int (x^(3)+x-x^(2)-1)dx` `=(x^(4))/(4)+(x^(2))/(2)-(x^(3))/(3)-x+c` `underset (x to 0)(lim)(log(f(x)))/(g(x))=underset(x to 0)(lim)(log(1+x^(2)))/(x+x^(3))` `=underset(x to 0)(lim)(log(1+x^(2)))/(x^(2))*(x^(2))/(x+x^(3))` `=underset(x to 0)(lim)(x)/(1+x^(2))=0` |
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