Question 34 of 70intermediate🔧 ApplyShort Answer2 marks

In each of the Exercises 1 to 9, find the coordinates of the foci, the vertices, the length of major axis, the minor axis, the eccentricity and the length of the latus rectum of the ellipse: 36x² + 4y² = 144

Correct Answer

The given equation is 36x2+4y2=14436x^2 + 4y^2 = 144.

Step 1: Converting to standard form

Dividing both sides by 144:

36x2144+4y2144=1\frac{36x^2}{144} + \frac{4y^2}{144} = 1 x24+y236=1\frac{x^2}{4} + \frac{y^2}{36} = 1

Step 2: Identifying a and b

Since the denominator of y236\frac{y^2}{36} is larger than the denominator of x24\frac{x^2}{4}, the major axis is along the y-axis.

Comparing with x2b2+y2a2=1\frac{x^2}{b^2} + \frac{y^2}{a^2} = 1:

  • a2=36a^2 = 36, so a=6a = 6
  • b2=4b^2 = 4, so b=2b = 2

Step 3: Calculating c and eccentricity

c=a2−b2=36−4=32=42c = \sqrt{a^2 - b^2} = \sqrt{36 - 4} = \sqrt{32} = 4\sqrt{2}

Eccentricity e=ca=426=223e = \frac{c}{a} = \frac{4\sqrt{2}}{6} = \frac{2\sqrt{2}}{3}

Step 4: Finding all parameters

  • Foci: (0,±42)(0, \pm 4\sqrt{2}) i.e., (0,42)(0, 4\sqrt{2}) and (0,−42)(0, -4\sqrt{2})
  • Vertices: (0,±6)(0, \pm 6) i.e., (0,6)(0, 6) and (0,−6)(0, -6)
  • Length of major axis: 2a=122a = 12 units
  • Length of minor axis: 2b=42b = 4 units
  • Eccentricity: 223\frac{2\sqrt{2}}{3}
  • Length of latus rectum: 2b2a=2×46=43\frac{2b^2}{a} = \frac{2 \times 4}{6} = \frac{4}{3} units
Exercise: EXERCISE 10.3 | Q: 7 | (Page 20)
For More Understanding

Explanation

This question requires converting the ellipse equation to standard form to identify the major and minor axes. Since the coefficient of y² has a larger denominator (36 > 4), the major axis is along the y-axis. The solution follows the same method as shown in Example 9 of the textbook context, where comparing denominators determines the axis orientation.

Solution Steps

  1. Step 1: Divide equation by 144 to get standard form x²/4 + y²/36 = 1

  2. Step 2: Identify a² = 36, b² = 4, so a = 6, b = 2 (major axis along y-axis)

  3. Step 3: Calculate c = a2−b2\sqrt{a² - b²} = 32\sqrt{32} = 42\sqrt{2}

  4. Step 4: Calculate eccentricity e = c/a = 22\sqrt{2}/3

  5. Step 5: Find foci (0, ±42\sqrt{2}), vertices (0, ±6), major axis = 12, minor axis = 4, latus rectum = 4/3