# Find The Y Intercept - Urgent

• Jun 25th 2007, 08:13 PM
mibamars
Find The Y Intercept - Urgent
I need serious help.

I need to find the Y intercept of the graph

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

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

• Jun 25th 2007, 08:15 PM
Jhevon
for the y-intercept, just plug in x = 0
• Jun 25th 2007, 08:17 PM
mibamars
Awesome. Any help with the others?
• Jun 25th 2007, 08:29 PM
Jhevon
Quote:

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

I also need to X when y=3

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

when $\displaystyle y = 3$ we have

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

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

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:

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

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

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

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?