Quadratic Problem.

(Wondering)
Ok this is what the problem is

In 1900, one of the most devastating hurricanes in the United States occurred in Galveston. The people of the city had prior warning, but many waited to leave the island until teh streets and the only bridge were covered with 4 feet of water. The winde speed reached 220 mph. Five foot waves destroyed wooden buildings and carried the occupants out to the sea. Use your equation to find a level for hurricanes reaching this wind speed.

Level - Maximum Wind Speed(mph)
1 - 95
2 - 110
3 - 130
4 - 155

The equation i found was y=2.5x^2+7.5x+85

My teach said plug 220 into it like so:
220=2.5x^2+7.5x+85
-220 -220

0=2.5x^2+7.5x-135

Now im lost... anyone know how to do this?

You just have to solve for X now, by the quadratic formula

Quote:

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Originally Posted by jemadd2

(Wondering)
Ok this is what the problem is

In 1900, one of the most devastating hurricanes in the United States occurred in Galveston. The people of the city had prior warning, but many waited to leave the island until teh streets and the only bridge were covered with 4 feet of water. The winde speed reached 220 mph. Five foot waves destroyed wooden buildings and carried the occupants out to the sea. Use your equation to find a level for hurricanes reaching this wind speed.

Level - Maximum Wind Speed(mph)
1 - 95
2 - 110
3 - 130
4 - 155

The equation i found was y=2.5x^2+7.5x+85

My teach said plug 220 into it like so:
220=2.5x^2+7.5x+85
-220 -220

0=2.5x^2+7.5x-135

Now im lost... anyone know how to do this?

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$\displaystyle 2.5x^2+7.5x-135=0$

Divide the equation by 2.5, we get,

$\displaystyle x^2+3x-54=0$

$\displaystyle (x+6)(x-3)=0$

$\displaystyle x= -6, x=3$

thanks for that but i will get two answers when i do that because of the + i will get 1350 for + and
i will get 1335 for - what do i do with these two? divide?

I did a guess check and found that 6 works with it... which would make it

LEVEL=Mph
6=220mph

If someone knows how to figure out x when y is given. plz post for me.

P.S. i need 1 answer. not x=?,x=?(Headbang)