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binomial theoram — MATHS STD 11 Science — Question

Gujarat BoardEnglish MediumSTD 11 ScienceMATHSbinomial theoram1 Mark
MCQ
If ${(a + bx)^{ - 2}} = \frac{1}{4} - 3x + ......$, then $(a,b)$=
  • ✓
    $(2, 12)$
  • B
    $( - 2,12)$
  • C
    $(2,\,\, - 12)$
  • D
    None of these
✓

Answer

Correct option: A.
$(2, 12)$
a
(a) ${(a + bx)^{ - 2}} = \frac{1}{{{a^2}}}{\left( {1 + \frac{b}{a}x} \right)^{ - 2}} = \frac{1}{{{a^2}}}\left[ {a + \frac{{( - 2)}}{{1!}}\left( {\frac{b}{a}} \right)x + ....} \right]$

Equating it to $\frac{1}{4} - 3x + ....,$ we get $a = 2,b = 12$.

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