Solve Quadratic Equations: Math Grade 11 Help

[punk_rawk_jazz]

This question comes from a section on "Solving Problems With Quadratic Equations." I'm having problems with this, and I can't figure out why I can't get the right answer.

The length of a rectangle is 9cm longer than it's width. The area of the rectangle is 90 cm^2. Find the dimensions of the rectangle.

I drew a digram with the information. I used the formula to find area which is a=lw. The width of this is 'X'. The length is 'X+9'. The area is 90cm^2. I could not get the right answer for this. I set it up as 90=(x)(x+9) Then solved for x. The answer that I got was 81. The answer that I was supposed to get was 6. Anyone have any ideas of what I did wrong?
Thanks in advance for the help!

 

[brass]

your setup is good...how did you solve for x?

I might suggest distributing the x, setting the quadratic to zero, and factoring.

 

[himanshu121]

the quadratic eqn is
$$x^2+9x-90=0$$
$$x^2+15x-6x-90=0$$
$$(x+15)(x-6)=0$$
so x=6
hope it satisfies u

 

[punk_rawk_jazz]

I distributed x. but forgot to set the quadratic to zero. But after I did that. I got that x=-10 and x=9... That's still wrong... Any ideas?

 

[punk_rawk_jazz]

Thanx. Got it now.

 

[jai6638]

Wow.. this is grade 11 math?? i did this in grade 9...

 

[jayess]

guys, i have a unit test tomorrow, and i really need some help with these practice questions! can you please help ?!

1)which row in pascals triangle has the sum of 16384. show your work

2)How many times can you spell math rocks if it's written in pascals triangle form? explain.

3)Jamal works at a toy factory, on his 20th day working he made 137 toys, he noticed that each day, he makes 3 more toys than the day before. what is the sum of the amount of toys jamal has made?

4) a. if t=10, find the first 4 terms

b. ^ find the explicit formula for the terms.

5) what's the sum if, 3,+ 7, + 11, ... + 71.

 

[ideasrule]

guys, i have a unit test tomorrow, and i really need some help with these practice questions! can you please help ?!

1)which row in pascals triangle has the sum of 16384. show your work

2)How many times can you spell math rocks if it's written in pascals triangle form? explain.

3)Jamal works at a toy factory, on his 20th day working he made 137 toys, he noticed that each day, he makes 3 more toys than the day before. what is the sum of the amount of toys jamal has made?

4) a. if t=10, find the first 4 terms

b. ^ find the explicit formula for the terms.

5) what's the sum if, 3,+ 7, + 11, ... + 71.

We're not going to help unless you show your best attempt at all of the questions. Also, please start a new thread, preferably in Precalculus and not in Introductory Physics, instead of hijacking someone else's.