AP EAMCET · Maths · Binomial Theorem

If $' a'$ is the middle term in the expansion of $(2 x - 3 y)^{8}$ and $b, c$ are the middle terms in the expansion of $(3 x + 4 y)^{7},$ then the value of $\frac{b + c}{a},$ when $x = 2$ and $y = 3,$ is

A $\frac{1}{2}$
B $\frac{2}{3}$
C $1$
D $2$

Verified Solution

Answer & Solution

Correct Answer

(D) $2$

Step-by-step Solution

Detailed explanation

It is given that x=2, y=3 By the expansion of (2x-3y)8 middle term is 5th term. a=C48(2x)4(3y)4(-1)4 ⇒a=8!4!4!×24×34×x2y2 =70×24×34×24×34 Similarly, in the expansion of (3x+4y)7, 4th and 5th terms are middle terms.…

Apply the relevant identity from the chapter and substitute the values established in the previous step, keeping the original constraint in view.

Use the simplified expression to isolate the unknown, then plug the result back into the question setup to confirm the working is internally consistent.

Cross-check against a boundary or limiting case. Both the dimensional balance and the qualitative behaviour at the extreme should agree with the candidate answer.

Combine the steps above to identify the correct option. The remaining choices each fail at least one of the consistency, dimensional, or boundary checks.

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If 'a' is the middle term in the expansion of (2x-3y)8 and b, c are the middle terms in the expansion of (3x+4y)7, then the value of b+ca, when x=2 and y=3, is

Step-by-step Solution

If $' a'$ is the middle term in the expansion of $(2 x - 3 y)^{8}$ and $b, c$ are the middle terms in the expansion of $(3 x + 4 y)^{7},$ then the value of $\frac{b + c}{a},$ when $x = 2$ and $y = 3,$ is