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Question

If a + b = 7 and ab = 12, then \(a^2 + b^2\) is equal to:

This question was previously asked in
RRB ALP/Technician 2018 CBT 2 Electronics Mechanic Question Paper (23-Jan-2019) (Shift 1)
The correct answer is
25

Solving for \(a^2 + b^2\) Algebraically

We are given two equations:

  • \(a + b = 7\)
  • \(ab = 12\)

We need to find the value of \(a^2 + b^2\). We can use the algebraic identity related to the square of a sum:

\( (a+b)^2 = a^2 + 2ab + b^2 \)

Applying the Identity

To find \(a^2 + b^2\), we can rearrange the identity:

\( a^2 + b^2 = (a+b)^2 - 2ab \)

Substitution and Calculation

  1. Substitute the given values into the rearranged formula:
    • \(a+b = 7\)
    • \(ab = 12\)
    So, the equation becomes:

    \( a^2 + b^2 = (7)^2 - 2(12) \)

  2. Calculate the squares and products:

    \( (7)^2 = 49 \)

    \( 2(12) = 24 \)

  3. Perform the subtraction:

    \( a^2 + b^2 = 49 - 24 \)

    \( a^2 + b^2 = 25 \)

Therefore, the value of \(a^2 + b^2\) is 25.

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Similar Questions

  1. For what value of K is the equation \(\frac{0.009}{K} = 0.1\) true?
  2. Arnab buys 9 oranges and 8 bananas for ₹276. When the cost of an orange is decreased by 10% and that of a banana remains the same, then the cost of 5 oranges and 10 bananas is ₹210. What is the original cost of 4 oranges and 3 bananas?
  3. Reduce to linear form 

    \(\frac{5x + 1}{2x} = \frac{5}{4}\)

  4. The value of (x - y)(x + y) + (y - z)(y + z) + (z - x)(z + x) is:

  5. What is the product of (x + a) and (x + b)?

  6. A 3-digit number is such that the units' digit, the tens' digit, and the hundreds' digit are in the ratio 1 : 2 : 3. The sum of this number and the number obtained by writing its digits in reverse order is 1332. Find the number.

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Important Questions from Algebric Equations

  1. For what value of K is the equation \(\frac{0.009}{K} = 0.1\) true?
  2. Arnab buys 9 oranges and 8 bananas for ₹276. When the cost of an orange is decreased by 10% and that of a banana remains the same, then the cost of 5 oranges and 10 bananas is ₹210. What is the original cost of 4 oranges and 3 bananas?
  3. Find the value of x satisfying: $5(5x^2 - 5) - 5(5x^2 + 7x - 2) = 14$
  4. The product of two positive numbers is 3645. If the first number is five times the second number, then the sum of the two numbers is:
  5. The product of two positive numbers is 80. If the first number is five times of the second number, then the sum of the two numbers is:
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