Determine The Value Of A
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The gradient of the curve $=\frac{a}{10}+bx^2$ at the point (iii,6) is 7. Calculate the values of a and b.
I did it,
$half-dozen=\frac{a}{3}+b(three^ii) \tag{1} $ We also have: (derivative) $y'=-\frac{a}{ten^2}+2bx \tag{ii}$
$7=-\frac{a}{3^ii}+2b(3) \tag{3} $
but it doesn't seen right.
the answer is a=-9, b=1
Can you lot help me out? cheers.
asked April 13, 2012 at 1:28
Cin Sb SangpiCin Sb Sangpi
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5
ii Answers two
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From $half dozen=\frac a3+9b$ it follows that $a=18-27b$. Substituting into (3) we get $seven=-\frac{eighteen-27b}{9}+6b=3b-two+6b$, hence $b=i$ and $a=eighteen-27=-9$.
answered Apr 13, 2012 at one:38
azarelazarel
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6
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$\begingroup$ At the time of this annotate, your reputation is $3935$, and mine is $3539$... interesting! $\endgroup$
April 13, 2012 at 1:43
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$\begingroup$ @TheChaz A fleck strange indeed. $\endgroup$
Apr 13, 2012 at 1:47
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$\begingroup$ how did $a=18-27b$, i got only $18=a+27b$, thx. $\endgroup$
Apr 13, 2012 at 1:58
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$\begingroup$ Sb, if you lot don't know how to go from $$eighteen = a + 27b$$ to $$a = 18 -27b$$, and so nosotros might take a trouble! $\endgroup$
April 13, 2012 at 2:01
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$\begingroup$ aww..i see, so sorry, $a+27b=18$ and so $a=eighteen-27b$ $\endgroup$
Apr 13, 2012 at 2:05
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If you multiply equation (3) by 3, so add information technology to equation (1), yous'll get $$27 = 27b$$
From this, the value of $a$ follows.
answered Apr xiii, 2012 at 1:40
The Chaz ii.0The Chaz 2.0
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Determine The Value Of A,
Source: https://math.stackexchange.com/questions/131120/calculate-the-value-of-a-and-b
Posted by: couturedoemput.blogspot.com
$\begingroup$ In equation $(1)$ a $b$ is missing. $\endgroup$
–user21436
Apr 13, 2012 at one:34
$\begingroup$ Your values of $a$ and $b$ are right. $\endgroup$
–user21436
April 13, 2012 at 1:36
$\begingroup$ Why practise you think you lot could be wrong? Anything particular you're doubtful almost? $\endgroup$
–user21436
Apr 13, 2012 at one:38
$\begingroup$ yep, i don't know how to exercise farther. thx :) $\endgroup$
April 13, 2012 at i:42
$\begingroup$ Information technology was not clear if yous wanted us to check the answer or how to get that answer? Oh, well, there are answers now. $\endgroup$
–user21436
Apr 13, 2012 at 1:44