Lenght of rectangle is 7 cm less than 4 times its width. Area is 36, find dimensions. Is this set up right? : 4x-7=36

- anonymous

- schrodinger

I got my questions answered at brainly.com in under 10 minutes. Go to brainly.com now for free help!

At vero eos et accusamus et iusto odio dignissimos ducimus qui blanditiis praesentium voluptatum deleniti atque corrupti quos dolores et quas molestias excepturi sint occaecati cupiditate non provident, similique sunt in culpa qui officia deserunt mollitia animi, id est laborum et dolorum fuga.
Et harum quidem rerum facilis est et expedita distinctio. Nam libero tempore, cum soluta nobis est eligendi optio cumque nihil impedit quo minus id quod maxime placeat facere possimus, omnis voluptas assumenda est, omnis dolor repellendus.
Itaque earum rerum hic tenetur a sapiente delectus, ut aut reiciendis voluptatibus maiores alias consequatur aut perferendis doloribus asperiores repellat.

Get this expert

answer on brainly

SEE EXPERT ANSWER

Get your **free** account and access **expert** answers to this

and **thousands** of other questions

- asnaseer

not quite - the question says that the length is 7cm less than 4 times its width, so if we call the length y and the width x, then you can write:
y = 4x - 7
It also says the area is 36, so we know the area of a rectangle is length times width, therefore:
xy = 36
Now you have two equations with two unknowns so you should be able to solve this to find x and y.

- anonymous

What do you mean by that? How can i set it up to solve?

- asnaseer

substitute the expression for y from the first equation into the second equation. that will give you a quadratic equation in x to solve.

Looking for something else?

Not the answer you are looking for? Search for more explanations.

## More answers

- anonymous

ok be right back.. :)

- anonymous

is answer 165?

- asnaseer

the question was asking for the dimensions of the rectangle - so you need an answer for x and y.

- anonymous

ok im back

- asnaseer

so how did you get 165?

- anonymous

i put it into the top equation the area

- anonymous

The length of a rectanlge is 7 cm less than 4 times its width. Its area is 36, find dimensions

- anonymous

I put it down here to make it easier for you

- asnaseer

we have two equations:\[y=4x-7\tag{a}\]and:\[xy=36\tag{b}\]if we substitute the expression for y from equation (a) into equation (b) we get:\[x(4x-7)=36\]\[4x^2-7x=36\]\[4x^2-7x-36=0\]this is a quadratic equation which you should be able to factor (or use the quadratic equation formula) to find the two possible answers for x.

- anonymous

do i use bottom equation to solve now :D and two ( ) are my answer? :D

- asnaseer

you need to solve:\[4x^2-7x-36=0\]this will give you two possible answers for x. one will be a positive value and the other will be a negative value. since a rectangle cannot have a negative length you can reject the negative solution. you will therefore be left with one answer for x. plug this value of x back into equation (a) above to find the corresponding value for y.
that will then give you the dimensions of the rectangle.

- anonymous

4 and -9/4? :/

- asnaseer

correct values for x: now you can reject the negative value as I stated above.

- anonymous

so i take out negative so its only 9/4

- anonymous

is the answer 4 and 9?

- asnaseer

no. the quadratic equation gave you two possible solutions for x.
one of these was x=4 and the other was x=-9/4.
since a rectangle cannot have a negative length, you can reject the solution x=-9/4.
you are therefore left with x=4 as the only valid solution for the width of the rectangle.
plug this value of x into equation (a) above to get the correct valid value for the length y of the rectangle.

- anonymous

I think i understand now but can you give me the answer? :( I wont ask again, its just this stupid program im using keeps knocking me off and giving me new questions, the server is freaking out and if i leave it sitting for awhile trying to figure it out it makes me start over, which is unfair

- asnaseer

the last step is very easy - you should be able to calculate it yourself.

- anonymous

what do i substitute 4 into again?

- asnaseer

equation (a) above

- asnaseer

substitute x=4 into:
y = 4x - 7

- anonymous

so its y=4(4)-7? gets y

- asnaseer

yes

- anonymous

answer is 9?

- anonymous

4 then 9?

- asnaseer

yes, so length of rectangle is 9 and width is 4

- anonymous

thank you :)

- asnaseer

yw

Looking for something else?

Not the answer you are looking for? Search for more explanations.