Respuesta :

  • The sides of a rectangle with area 12cm² are (3x-2) and (x+1).
  • We know, area of a rectangle = length × breadth
  • Therefore, by the problem

[tex](3x - 2)(x + 1) = 12 \\ = > {3x}^{2} - 2x + 3x - 2 = 12 \\ = > {3x}^{2} + x - 2 = 12 \\ = > {3x}^{2} + x - 12 - 2 = 0 \\ = > {3x}^{2} + x - 14 = 0 \\ = > {3x}^{2} + 7x - 6x - 14 = 0 \\ = > x(3x + 7) - 2(3x + 7) = 0 \\ = > (x - 2)(3x + 7) = 0 \\ = > x = 2 \: \: \: or \: \: \: \frac{ - 7}{3} \\ [/tex]

  • But a negative number cannot be the side of a rectangle.
  • So, x = 2 cm
  • Now, length = (3x - 2) = (3 × 2 - 2) cm = (6 - 2) cm = 4 cm
  • Breadth = (x + 1) = (2 + 1) cm = 3 cm.
  • We know, perimeter of a rectangle = 2( length + breadth)
  • Therefore, the perimeter of the rectangle

[tex] = 2(4 + 3)cm \\ = 2 \times 7cm \\ = 14cm[/tex]

Answer:

The value of x is 2 cm and the perimeter of the rectangle is 14 cm.

Hope you could get an idea from here.

Doubt clarification - use comment section.

ivylovesmaths
So first of all u have to make an equation. u know that length times width is the area 12. (3x-2) multiplied by (x+1) which is 3x^2+3x-2x-2 then simplified its 3x^2+x-2. THEN MAKE IT EQUAL TO 12 BC 12 IS THE AREA. so 3x^2+x-2=12 then use the quadratic formula to find x u can either use quadratic formula or factorising. I used factorising to get (x-2)(3x+7)=0 x=2 or x=-7/3. Sub in 2 into the equation 3x^2+x-2=12 to get 3(2)^2+2-2=12 so it will be 36+2=38 and then 38-2=36. That doesn’t sum up 12 so that isnt x. Then sub in -7/3 as x. So 3(-7/3)^2+(-7/3)-2. When u multiple that out it will give you 12. SO X IS 12. Then to work out the perimeter double the sides given (3x-2) and (x+1). That will be 6x-4+2x+2. Simplify to get to 8x-2. Then sub in your x (-7/3) to get 392/9. If u want u can leave it as a fraction or decimal 43.55555… where 5 is recurring. That is your perimeter. It looks confusing but trust me you will get :). Thank you

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