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Work out. 1 1/5 + 2 1/3 m = 2 x 3^a x 7^b and n = 3 x 72 x 11 Given that m > 126, find the smallest values of a and b which make m a multiple of 126. Explain why 33n is a perfect square.

Mathematics

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Step-by-step solution

8 steps

Here are the solutions to the problems:

1. Work out 115+2131\frac{1}{5} + 2\frac{1}{3}

Step 1: Convert the mixed numbers to improper fractions.

115=1×5+15=651\frac{1}{5} = \frac{1 \times 5 + 1}{5} = \frac{6}{5} 213=2×3+13=732\frac{1}{3} = \frac{2 \times 3 + 1}{3} = \frac{7}{3}

Step 2: Find a common denominator for the fractions, which is 15.

65=6×35×3=1815\frac{6}{5} = \frac{6 \times 3}{5 \times 3} = \frac{18}{15} 73=7×53×5=3515\frac{7}{3} = \frac{7 \times 5}{3 \times 5} = \frac{35}{15}

Step 3: Add the fractions.

1815+3515=18+3515=5315\frac{18}{15} + \frac{35}{15} = \frac{18 + 35}{15} = \frac{53}{15}

Step 4: Convert the improper fraction back to a mixed number.

5315=3815\frac{53}{15} = 3\frac{8}{15}

The final answer is 3815\boxed{\mathbf{3\frac{8}{15}}}.

2. Given m=2×3a×7bm = 2 \times 3^a \times 7^b and n=3×72×11n = 3 \times 7^2 \times 11

Part a· 4 steps

Given that m>126m > 126, find the smallest values of aa and bb which make mm a multiple of 126.

  1. Find the prime factorization of 126.

    126=2×63=2×9×7=21×32×71126 = 2 \times 63 = 2 \times 9 \times 7 = 2^1 \times 3^2 \times 7^1
  2. For m=2×3a×7bm = 2 \times 3^a \times 7^b to be a multiple of 126=21×32×71126 = 2^1 \times 3^2 \times 7^1, the exponents of its prime factors must be greater than or equal to those of 126.

    For the prime factor 2: 212^1 in mm matches 212^1 in 126.
    For the prime factor 3: 3a3^a in mm means a≥2a \ge 2.
    For the prime factor 7: 7b7^b in mm means b≥1b \ge 1.

  3. Consider the condition m>126m > 126.

    If we take the smallest possible values from Step 2 (a=2,b=1a=2, b=1), then m=2×32×71=2×9×7=126m = 2 \times 3^2 \times 7^1 = 2 \times 9 \times 7 = 126.
    This value of mm is not strictly greater than 126, so we need to increase mm. To do this, we must increase either aa or bb by at least 1.

  4. Find the smallest aa and bb that satisfy a≥2a \ge 2, b≥1b \ge 1, and m>126m > 126.

    Let's test the smallest possible value for aa, which is a=2a=2.
    If a=2a=2, then m=2×32×7b=18×7bm = 2 \times 3^2 \times 7^b = 18 \times 7^b.
    We need 18×7b>12618 \times 7^b > 126.
    Divide by 18: 7b>12618=77^b > \frac{126}{18} = 7.
    So, 7b>717^b > 7^1, which implies b>1b > 1.
    Since bb must be an integer and b≥1b \ge 1, the smallest integer value for bb that satisfies b>1b > 1 is b=2b=2.
    Therefore, the smallest values are a=2a=2 and b=2b=2.
    Let's check this: m=2×32×72=2×9×49=18×49=882m = 2 \times 3^2 \times 7^2 = 2 \times 9 \times 49 = 18 \times 49 = 882.
    882 is a multiple of 126 (882=7×126882 = 7 \times 126) and 882>126882 > 126.

    The final answer is a=2,b=2\boxed{\mathbf{a=2, b=2}}.

Part b· 4 steps

Explain why $33n$ is a perfect square.

  1. Substitute the expression for nn into 33n33n.

    Given n=3×72×11n = 3 \times 7^2 \times 11.

    33n=33×(3×72×11)33n = 33 \times (3 \times 7^2 \times 11)
  2. Express 33 as a product of its prime factors.

    33=3×1133 = 3 \times 11
  3. Substitute the prime factors of 33 into the expression for $33n$ and combine like terms.

    33n=(3×11)×(3×72×11)33n = (3 \times 11) \times (3 \times 7^2 \times 11) 33n=31×111×31×72×11133n = 3^1 \times 11^1 \times 3^1 \times 7^2 \times 11^1 33n=31+1×72×111+133n = 3^{1+1} \times 7^2 \times 11^{1+1} 33n=32×72×11233n = 3^2 \times 7^2 \times 11^2
  4. Explain why the result is a perfect square.

    A number is a perfect square if all the exponents in its prime factorization are even. In the expression 32×72×1123^2 \times 7^2 \times 11^2, all the exponents (2, 2, and 2) are even.
    Therefore, 33n33n is a perfect square. It can also be written as (3×7×11)2=(231)2(3 \times 7 \times 11)^2 = (231)^2.

    The final answer is Because the prime factorization of 33n is 32×72×112, where all prime factors have even exponents.\boxed{\text{Because the prime factorization of } 33n \text{ is } 3^2 \times 7^2 \times 11^2, \text{ where all prime factors have even exponents.}}

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