Rational Numbers | FIO

Question 3

Given 1252=15625125^2 = 15625, what is the value of 1262126^2?

(i) 15625 + 126

(ii) 15625+26215625 + 26^2

(iii) 15625 + 253

(iv) 15625 + 251

(v) 15625+51215625 + 51^2

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Solution

An algebraic identity helps us find the square of a number easily.

Step 1 — Express the number

We are given the value of 1252125^2. We need to find the value of 1262126^2. We can write 126126 as the sum of two numbers. Let us write 126126 as 125+1\mathbf{125 + 1}.

Step 2 — Apply the identity

We will use a special rule called an algebraic identity. This rule helps us square a sum of two numbers. The identity is (a+b)2=a2+2ab+b2(a+b)^2 = a^2 + 2ab + b^2. Here, we can think of aa as 125\mathbf{125}. We can think of bb as 1\mathbf{1}. Let us substitute these values into the identity.

1262=(125+1)2126^2 = (125 + 1)^2

=1252+(2×125×1)+12= 125^2 + (2 \times 125 \times 1) + 1^2

=15625+250+1= 15625 + 250 + 1

=15625+251= 15625 + 251

15876\boxed{15876}

We found that 1262126^2 is 15625+251\mathbf{15625 + 251}. This matches option (iv).

Answer

(iv) 15625+25115625 + 251

More questions in FIO

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(i) 2032 (ii) 2048 (iii) 1027 (iv) 1089

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Q3

Given 1252=15625125^2 = 15625, what is the value of 1262126^2?

(i) 15625 + 126

(ii) 15625+26215625 + 26^2

(iii) 15625 + 253

(iv) 15625 + 251

(v) 15625+51215625 + 51^2

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Q12

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(i) The cube of any odd number is even.

(ii) There is no perfect cube that ends with 8.

(iii) The cube of a 2-digit number may be a 3-digit number.

(iv) The cube of a 2-digit number may have seven or more digits.

(v) Cube numbers have an odd number of factors.

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You are told that 1331 is a perfect cube. Can you guess without factorisation what its cube root is? Similarly, guess the cube roots of 4913, 12167, and 32768.

Q14

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