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Case Study 3: Number system Case Study Class 9

An astronomer named Dr. Sarah is studying the movement of a distant comet using a high-powered telescope. She records the time interval between two specific flashes of light as 0.45̅ seconds. Dr. Sarah explains to her interns that because this decimal is recurring, it is a rational number and can be used in their primary calculations. To mark the comet’s trajectory relative to a fixed star, she uses a coordinate system where the star is at position 0. She marks a specific gravitational point at √5 units on the number line, which she locates by constructing a right-angled triangle with a base of 2 units and a height of 1 unit.

The interns are tasked with calculating the light intensity reduction as the comet passes through a gas cloud. The reduction factor is given by the expression 1 / (√3 + √2). To simplify the sensor data, they must rationalize the denominator. Additionally, the mass of the comet’s nucleus is estimated using an exponential formula: (163/4 · 2-2) ÷ 2. The interns must simplify this to a single integer for the final report. During their observations, they also find a specific wavelength ratio that results in 1.41421356…, a value that never ends and never repeats, which they must categorize correctly to determine the comet’s composition.

1. Dr. Sarah wants to convert the time interval 0.45̅ into a fraction p/q. Which of the following is the correct simplest form?
Solution: Let x = 0.4545… (i). Since two digits repeat, multiply by 100: 100x = 45.4545… (ii). Subtract (i) from (ii): 99x = 45 ⇒ x = 45/99. Dividing by 9: x = 5/11.
2. To represent √5 on the number line, the interns use a triangle with base 2 and height 1. If the base starts at 0, the hypotenuse will represent:
Solution: Using Pythagoras theorem: H² = 2² + 1² = 4 + 1 = 5. Thus, H = √5.
3. Simplify the light intensity reduction factor by rationalizing the denominator: 1 / (√3 + √2).
Solution: Multiply numerator and denominator by the conjugate (√3 – √2): [1 * (√3 – √2)] / [(√3)² – (√2)²] = (√3 – √2) / (3 – 2) = √3 – √2.
4. Find the simplified value for the mass estimate of the nucleus using laws of exponents: (163/4 · 2-2) ÷ 2.
Solution: 163/4 = (2⁴)3/4 = 2³ = 8. Then (8 · 1/4) ÷ 2 = 2 ÷ 2 = 1.
5. The wavelength ratio 1.41421356… is non-terminating and non-recurring. Under which category does this number fall?
Solution: Numbers whose decimal representation is non-terminating and non-repeating are called irrational numbers.
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