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Let $a_{r}$ denote the coefficient of $y^{r - 1}$ in the expansion of ${(1 + 2 y)}^{10}$ . If $\frac{a_{r + 2}}{a_{r}} = 4$ , then $r$ is equal to

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Correct option is D

Tr+1=10Cr(2y)r= 10Cr2ryr.∴ ar=10Cr2rNow 4=ar+2ar= 10Cr+2 10Cr2r+22r⇒ 10Cr+2=10Cr⇒r+2=10−r⇒r=4

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Let ar denote the coefficient of yr-1 in the expansion of (1+2y)10. If ar+2ar=4, then r is equal to

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Let $a_{r}$ denote the coefficient of $y^{r - 1}$ in the expansion of ${(1 + 2 y)}^{10}$ . If $\frac{a_{r + 2}}{a_{r}} = 4$ , then $r$ is equal to