Question

The length of a rectangle is 2m more than the width. The area of the rectangle is 20 m^2. Find the dimensions of the rectangle, to the nearest tenth of a metre.

Answer 1

The answer is 3.6 m by 5.6m... how?

Answer 2

We know that for a rectangle, the area is length x width
A = l*w
We know that the length is 2 meters more than the width
So the the length minus 2 in the width => l - 2 = w
l = w + 2
Substitutin in the area formula:
A = (w+2)(w)
20 = w(w+2)
Solve for w using the quadratic equation, then using the w you can find l

Answer 3

solve for w using the quadratic equation? so it's going ot be w^2 + 2w - 20 = 0

Answer 4

yup

Answer 5

ohhhh,

Answer 6

Get it now? :)

Answer 7

yup! Oh, but what's a product of -20 and a sum -20? o.o

Answer 8

Product of -20, sum of 2...
Do you know how to use the quadratic equation?

Answer 9

sort of.. isn't it like factoring?

Answer 10

Its like factoring, but when like integer numbers dont work to solve the equation
http://www.oncalc.com/wp-content/uploads/2011/02/quadratic-equation-calculator.gif

Answer 11

You see that equation before?

Answer 12

ohhhh the quadratic formula?

Answer 13

Yeah, sorry didnt know what you call it

Answer 14

it's okay. But what about it? That's all I use after I've figured it's w^2 + 2w - 20 =0?

Answer 15

Yup, plug it in to the quadratic formula

Answer 16

ohh, thank you!

Answer 17

Okay, well I got -2 +/- 2sqr.rt:21/2 ...

Answer 18

punch that into a calculator and what do you get?

Answer 19

so I don't have to do 2(-2 +/- sqr.rt:21/2?

Answer 20

well what number do you get from that?

Answer 21

Like evaluate the expression

Answer 22

not the answer.

Answer 23

(-2 + sqrt ( 4 - 4(1)(-20) )/ 2

Answer 24

I got 3.58

Answer 25

if you do (-2 - sqrt ( 4 - 4(1)(-20) )/ 2 , you get a negative number, and can omit it because there is no such thing as negaive lengths