I want check my answer

Q 1 : If the second term = 6 and fifteenth = 25 of sequence find the first term ?

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- Jan 31st 2010, 09:58 AMr-soyI want check my answer
I want check my answer

Q 1 : If the second term = 6 and fifteenth = 25 of sequence find the first term ? - Jan 31st 2010, 10:06 AMskeeter
$\displaystyle a_n = a_1 + (n-1)d$

$\displaystyle a_2 = a_1 + d$

$\displaystyle 6 = a_1 + d$

$\displaystyle a_{15} = a_1 + 14d$

$\displaystyle 25 = a_1 + 14d$

$\displaystyle 19 = 13d$

$\displaystyle d = \frac{19}{13}$

$\displaystyle a_1 = 6 - d = 6 - \frac{19}{13} = \frac{59}{13}$ - Jan 31st 2010, 10:08 AMe^(i*pi)
No, because you haven't answered the question fully. You've been asked to find the first term

*a*but you found the common difference*d*.

Your working seems fine though. Simply sub your value of d into one of your original equations to find a.

$\displaystyle U_2 = a + d = 6 $ (eq1)

$\displaystyle U_{15} = a + 14d = 25$ (eq2)

Rearrange eq1:

$\displaystyle d = 6-a$ (eq3)

sub eq3 into eq2

$\displaystyle a+14(6-a) = 25$

$\displaystyle -13a = -59$

$\displaystyle a = \frac{59}{13}$ - Jan 31st 2010, 10:59 AMr-soy
thanks

- Jan 31st 2010, 11:07 AMe^(i*pi)