Respuesta :

Answer:

7*3

Step-by-step explanation:

a*b= area of rectangle

a+4=b

a(a+4)=21

a^2+4a-21=0

a=3 or a=-7

a length can't be negative so a=3

b is a+4 =3+4=7

ItzNila

Step-by-step explanation:

GIVEN:-

Area = 21cm^2

Let Breadth = x cm

UNDERSTANDING THE CONCEPT:-

According to your question,

If breadth = x cm , length will be ( x + 4 )cm.

FORMULA:-

Area = length × Breadth

SUBSTITUTION:-

[tex]21 = (x)(x + 4)[/tex]

[tex]0 = x {}^{2} - 4x - 21 \\ [/tex]

[tex]0 = x {}^{2} + 7x - 3x - 21 \\ [/tex]

[tex]0 = x(x + 7) - 3(x + 7) \\ [/tex]

[tex]0 = (x - 3)(x + 7) \\ [/tex]

[tex]x = 3[/tex]

(- 7 will be neglected)

Breadth = 3 cm

Length = x + 4

= 7 cm

SO, The dimensions of rectangle is 7cm,3cm

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