Math Problem Statement

Find the dimensions of a rectangle with area 105 cm² and perimeter 44 cm, where the length is greater than the width.

Solution

We are tasked with finding the dimensions of a rectangle given:

  1. Area = 105cm2105 \, \text{cm}^2
  2. Perimeter = 44cm44 \, \text{cm}
  3. Length (ll) is greater than Width (ww).

Step 1: Express relations

  1. Area Formula: lw=105l \cdot w = 105
  2. Perimeter Formula: 2(l+w)=442(l + w) = 44, which simplifies to: l+w=22l + w = 22

Step 2: Solve for dimensions

From l+w=22l + w = 22, we get: l=22wl = 22 - w

Substitute l=22wl = 22 - w into the area equation: (22w)w=105(22 - w) \cdot w = 105 Simplify: 22ww2=10522w - w^2 = 105 Rearrange into standard quadratic form: w222w+105=0w^2 - 22w + 105 = 0

Step 3: Solve quadratic equation

Use the quadratic formula: w=b±b24ac2aw = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a} Here, a=1a = 1, b=22b = -22, c=105c = 105. Plugging in: w=(22)±(22)24(1)(105)2(1)w = \frac{-(-22) \pm \sqrt{(-22)^2 - 4(1)(105)}}{2(1)} w=22±4844202w = \frac{22 \pm \sqrt{484 - 420}}{2} w=22±642w = \frac{22 \pm \sqrt{64}}{2} w=22±82w = \frac{22 \pm 8}{2}

Thus: w=22+82=15orw=2282=7w = \frac{22 + 8}{2} = 15 \quad \text{or} \quad w = \frac{22 - 8}{2} = 7

Step 4: Find ll

If w=7w = 7, then: l=227=15l = 22 - 7 = 15

If w=15w = 15, then: l=2215=7l = 22 - 15 = 7

Since l>wl > w, the dimensions are: l=15cm,w=7cm\boxed{l = 15 \, \text{cm}, \, w = 7 \, \text{cm}}


Final Answer:

  • Length: 15cm15 \, \text{cm}
  • Width: 7cm7 \, \text{cm}

Would you like a detailed breakdown of any step or further explanations?

Here are five related questions for practice:

  1. How do you derive the perimeter formula for a rectangle?
  2. What are the steps to factorize a quadratic equation?
  3. Can you use trial and error instead of the quadratic formula here?
  4. How does knowing area and one dimension help find the other?
  5. What happens if length equals width (square case)?

Tip: Always verify solutions by substituting back into the original equations!

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Math Problem Analysis

Mathematical Concepts

Algebra
Quadratic Equations
Geometry (Rectangles)

Formulas

Area formula: l * w = Area
Perimeter formula: 2(l + w) = Perimeter
Quadratic equation formula: ax^2 + bx + c = 0
Quadratic formula: w = (-b ± √(b² - 4ac)) / 2a

Theorems

Solving quadratic equations
Properties of rectangles (Area and Perimeter)

Suitable Grade Level

Grades 7-9