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Question

Find the height of a triangle where the base corresponding to that height is half of the height, and the area is $144$ cm$^2$.

The correct answer is
24 cm

Understanding the Triangle Problem

The question asks us to find the height of a specific triangle. We are given two pieces of information:

  • The area of the triangle is $144$ cm$^2$.
  • The base ($b$) corresponding to this height ($h$) is half the length of the height. This can be written as: $b = \frac{h}{2}$.

Our goal is to use this information and the formula for the area of a triangle to calculate the height.

Area Formula and Substitution

The formula for the area ($A$) of a triangle is:

$$A = \frac{1}{2} \times \text{base} \times \text{height}$$

Using variables, this is:

$$A = \frac{1}{2}bh$$

We know that $A = 144$ cm$^2$ and $b = \frac{h}{2}$. Let's substitute the relationship between the base and height into the area formula:

$$A = \frac{1}{2} \left( \frac{h}{2} \right) h$$

Now, simplify this expression:

$$A = \frac{1}{4} h^2$$

Solving for the Height

Now we can substitute the given area ($A = 144$) into the simplified formula and solve for $h$:

$$144 = \frac{1}{4} h^2$$

To isolate $h^2$, multiply both sides of the equation by 4:

$$144 \times 4 = h^2$$

$$576 = h^2$$

To find the height $h$, take the square root of both sides:

$$h = \sqrt{576}$$

Calculating the square root:

$$h = 24$$

So, the height of the triangle is $24$ cm.

Final Answer Verification

Let's check if this height works with the given conditions:

  • Height ($h$) = $24$ cm.
  • Base ($b$) = $\frac{h}{2} = \frac{24}{2} = 12$ cm.
  • Area ($A$) = $\frac{1}{2}bh = \frac{1}{2} \times 12 \times 24 = 6 \times 24 = 144$ cm$^2$.

The calculated area matches the given area, confirming our height is correct.

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Important Questions from Mensuration 2D (Notes)

  1. A 2 cm wide wooden strip is to be fixed on a photo of 40 cm x 30 cm size all along its four sides. What is the minimum length of the wooden strip required?
  2. $110$ मी. $\times 60$ मी. घास-आच्छादित आयताकार प्लॉट के अंदर चारों ओर $2$ मी. चौड़ा बजरी का रास्ता बनाना है। $₹2$ प्रति वर्ग मी. की दर से बजरी बिछाने का लागत ज्ञात कीजिए।
  3. The perimeter of a square is $596$ m. Its area (in m$^2$) is:
  4. A hollow spherical shell is made of a metal of density 4 g/cm$^3$. Its internal and external radius are 15 cm and 18 cm, respectively. What is the weight (in kg) of the shell?
    (Use $\pi = \frac{22}{7}$ and Density = $\frac{\text{Mass}}{\text{Volume}}$)
  5. Water flows out through a circular pipe whose internal diameter is 2 cm, at the rate of 4 metres per second into a cylindrical tank, the radius of whose base is 80 cm. By how much will the level of water rise in 16 minutes?
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