# Find The Y Intercept - Urgent

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• Jun 25th 2007, 09:13 PM
mibamars
Find The Y Intercept - Urgent
I need serious help.

I need to find the Y intercept of the graph

$y= -0.02(x^3 - 38x^2 + 441x - 1620)$

I also need to X when y=3

I also need to find the equation of the inclined path if it hasa gradient of 4/5

Please help :(
• Jun 25th 2007, 09:15 PM
Jhevon
for the y-intercept, just plug in x = 0
• Jun 25th 2007, 09:17 PM
mibamars
Awesome. Any help with the others?
• Jun 25th 2007, 09:29 PM
Jhevon
Quote:

Originally Posted by mibamars
$y= -0.02(x^3 - 38x^2 + 441x - 1620)$

I also need to X when y=3

$y= -0.02(x^3 - 38x^2 + 441x - 1620)$

when $y = 3$ we have

$3= -0.02(x^3 - 38x^2 + 441x - 1620)$

$\Rightarrow x^3 - 38x^2 + 441x - 1470 = 0$

Trying the factors of 1470, we realize that x = 14 is a root, so (x - 14) is a factor. Dividing the cubic by (x - 14) using long division, we obtain:

$x^3 - 38x^2 + 441x - 1470 = (x - 14) \left( x^2 - 24 x + 105 \right) = 0$

$\Rightarrow x - 14 = 0 \mbox { or } x^2 - 24x + 105 = 0$

$\Rightarrow x = 14 \mbox { or } x = \frac {24 \pm \sqrt {156}}{2}$

Quote:

Originally Posted by mibamars
I also need to find the equation of the inclined path if it hasa gradient of 4/5

when you say inclined path you mean tangent line right?