S-x-is-the-sum-of-49-terms-of-AP-The-first-term-is-1-2-x-3-and-the-difference-is-7-x-If-S-x-maximum-the-value-of-10-th-term-is-

Question Number 13075 by Joel577 last updated on 13/May/17

S (x) is the sum of 49 terms of AP

The first term is \frac{1}{2} x^{3} and the difference

is (7 - x)

If S (x) maximum, the value of 10^{th} term is \dots

Commented by ajfour last updated on 13/May/17

l o c a l m a x i m u m ? x = - 4 t h e n,

T_{10} = \frac{{(- 4)}^{3}}{2} + 9 [7 - (- 4)]

= - 32 + 99 = 67 .

Commented by Joel577 last updated on 13/May/17

How did u get x = - 4 ?

Commented by ajfour last updated on 13/May/17

S (x) = \frac{49}{2} {2 (\frac{x^{3}}{2}) + 48 (7 - x)}

\frac{d S}{d x} = \frac{49}{2} {3 x^{2} - 48} = 0

\Rightarrow x^{2} = 16

x = \pm 4 .

Commented by ajfour last updated on 13/May/17

Commented by Joel577 last updated on 13/May/17

t h a n k y o u v e r y m u c h

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