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7.Binomial Theorem
easy
${(a + b)^n}$ ના વિસ્તરણમાં ચોથાપદ નો સહગુણક 56 હોય, તો $n$ મેળવો.
A
$12$
B
$10$
C
$8$
D
$6$
Solution
(c) ${T_4} = {T_{3 + 1}}$
$ = \,{}^n{C_3}\,\,\,{a^{n – 3}}{b^3}$
==> ${}^n{C_3} = 56$
==> $\frac{{n!}}{{3\,!\,\,\,\left( {n – 3} \right)\,!}} = 56$
==> $n(n – 1)(n – 2) = 56.6$
==> $n(n – 1)(n – 2) = 8\,.\,7\,.\,6$
==> $n = 8$.
Standard 11
Mathematics