A quadratic equation.... help please?

2008-05-14 11:08 am
Question is:
The perimeter of a rectangle is 50 cm and its area is 154cm 2(Squared). Find the length and the width of the rectangle.

Could someone please solve this with the working out?

Thanks in advance.

回答 (11)

2008-05-14 12:20 pm
✔ 最佳答案
Given:
Perimeter of rectangle = 50 cm.
Area of the rectangle = 154 cm
Find L = length : W = width

Area of rectangle = L x W
L x W = 154 ====> eq 1
Perimeter of the rectangle = L + W + L + W
Perimeter of the rectangle = 2L + 2 W
2L + 2W = 50 cm
L + W = 25 cm === > eq 2

From eq 2
L + W = 25 cm === > eq 2
L = 25 - W

Substitute L to eq 1
L x W = 154 ====> eq 1

(25 - W ) x W =154
25W - (W)^2 =154

(W)^2 - 25W + 154 =0

(W +11) (W-14) =0

W = -11 & W= 14

Using W =14 and Substitute to eq 2
L + W = 25 cm === > eq 2
L + (14) = 25
L = 25 -14
L = 11

=============================================
Ans:
W = 14 then L = 11
=============================================
2008-05-14 6:17 pm
p= 2*(w + l) = 50
a = w*l = 154

2w +2l = 50

w*l = 154 => l = 154/w

=> 2w +2*154/w = 50

w +154/w = 25

w^2/w +154/w = 25
w^2 +154 = 25w
w^2 - 25w +154 = 0

use quadratic formula to solve for w

or complete the square

w^2 - 25w = -154
w^2 - 25w + 156.25 = -154 + 156.25 //add (half 25)^2 to each side

w^2 - 25w + 156.25 = 2.25
(w - 12.5)^2 = 2.25

w - 12.5 = square root(2.25)
w - 12.5 = +1.5, -1.5
w = +1.5 + 12.5, -1.5 + 12.5
w = 14, 11

using: w*l = 154

l = 154/w
l = 154/14 = 11
l = 154/11 = 14

so rectangle is 11 by 14
2008-05-14 7:13 pm
x = width
y = length

2(x + y) = 50
xy = 154

2(x + y) = 50
x + y = 25
y = 25 - x

xy = 154
x(25 - x) = 154
25x - x^2 = 154
x^2 - 25x + 154 = 0
(x - 14)(x - 11) = 0

x - 14 = 0
x = 14

x - 11 = 0
x = 11

2(x + y) = 50
14 + y = 25
y = 25 - 14
y = 11

2(x + y) = 50
11 + y = 25
y = 25 - 11
y = 14

∴ [x (width) = 14 , y (length) = 11] or [x (width) = 11 , y (length) = 14]
2008-05-14 6:50 pm
2x + 2y = 50
x y = 154
y = 154/x

2x + 308 / x = 50
2x² + 308 = 50x
2x² - 50x + 308 = 0
x² - 25x + 154
(x - 11)(x - 14) = 0
x = 11 , x = 14
2008-05-14 6:27 pm
let
p - perimeter
a - area
l - lenght of the rectangle
w - width of the rectangle

given:
p = 50cm
a = 142 cm^2

formula:
p = 2l + 2w
a = lw

substitute the given to the respective formulas
50 = 2l+2w
divide the above equation by GCF 2
25 = l + w
l = 25 - w

substitute l
154 = lw
154 = (25-w)w
distribute
154 = 25w - w^2

tranpose 25w and -w^2 to the right side of the equation
w^2 - 25w + 154 = 0
factor
(w - 14)(w - 11) = 0
w - 14 = 0
w = 14cm
l = 25 - w = 25 - 14 = 11cm

w-11 = 0
w = 11cm
l = 25 - w = 25 - 11 = 14 cm

hope that's okay
thanks
2008-05-14 6:24 pm
2(L+B) = 50
LB = 154

L = 154/B

So, 2L+2B = 50
So, 2*154/B + 2B = 50
Dividing throughout by 2 gives,
154/B + B = 25
So, (154+B2) = 25
So, B2 - 25B + 154 = 0
So, B2 - 14B - 11B + 154 = 0
So, B(B-14) - 11 (B-14) = 0
Taking common,
(B - 14)(B - 11) = 0
So, B-14 = 0 OR B-11 = 0
So, B = 14 or B = 11

If B = 14, L = 11 (using 2L+2B=50)
If B = 11, L = 14

But, length will always be greater than breadth, so L = 14 and B = 11
2008-05-14 6:23 pm
say, length and breadth of rectangle are l and b, resectively.
perimeter of rectangle=2(l+b)=50
ie, l+b=25.. ie, b=25-l
area of rectangle=lb=154
ie, l(25-l)=154
ie, 25l-l^2=154
ie, l^2-25l+154=0
ie, l^2-11l-14l+154=0
ie, l(l-11)-14(l-11)=0
ie,(l-14)(l-11)=0
l=11,14
as lb=154, so b=14,11
so, the length and breadth are 14,11 or 11,14.
2008-05-14 6:21 pm
half perimeter, w + l = 25
area : w*l = 154

2w*l = 308
(w + l)^2 = 25^2 = 625
w^2 + l^2 + 2w*l = 625
w^2 + l^2 = 625 - 308 = 317

w^2 + l^2 - 2w*l = 317 - 308 = 9 = (w - l)^2
w - l = 3
w + l = 25
==>
2w = 28 ==> w = 14, l = 11
2008-05-14 6:18 pm
Let y be the length of the rectangle.
Let x be the width of the rectangle.

Now, the perimeter is (y + y + x + x), right?

Therefore:

y + y + x + x = 50
2y + 2x = 50
2y = 50 - 2x

y = 25 - x

Now we have y by itself:

We also know that area is xy (length multiplied by width) so we have:

xy = 154

Remember, we established that y = 25 - x before so simply replace the y in the above equation with 25 - x

x(25 - x) = 154
25x - x^2 = 154
x^2 - 25x + 154 = 0

x = 11 or 14

Therefore, the width is 11cm or 14cm.

That means the rectangle has dimensions 11x14 cm.
2008-05-14 6:15 pm
x+y=25
xy=154
factors of 154 is 2,7,11
therefore the answer is

11,14


收錄日期: 2021-05-01 10:31:37
原文連結 [永久失效]:
https://hk.answers.yahoo.com/question/index?qid=20080514030852AAdixDx

檢視 Wayback Machine 備份