JEE Mains · Maths · STD 11 - 7. binomial theoram
If the coefficients of \(x^2\) and \(x^3\) are both zero, in the expansion of the expression \((1 + ax + bx^2) (1 -3x)^{t5}\) in powers of \(x\), then the ordered pair \((a, b)\) is equal to
- A \((-54, 315)\)
- B \((28, 861)\)
- C \((28, 315)\)
- D \((-21, 714)\)
Answer & Solution
Correct Answer
(C) \((28, 315)\)
Step-by-step Solution
Detailed explanation
Coefficient of \(x^{2}=^{15} C_{2} \times 9-3 a\left(^{15} C_{1}\right)+b=0\) \(\Rightarrow^{15} \mathrm{C}_{2} \times 9-45 \mathrm{a}+\mathrm{b}=0.........(1)\) Coefficient of…
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