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Q7(ii):
Evaluate the following using suitable identities: (ii) $(102)^3$

Solution :

Initial Setup & Algebraic Identity Selection

We are tasked with evaluating the expression $(102)^3$ without performing direct multiplication. To achieve this, we utilize standard algebraic identities by expressing the base number as a binomial.

Step 1: Decomposition of the Base Number

To simplify the calculation, we decompose the base number $102$ into the sum of two numbers. It is computationally optimal to choose a multiple of $10$ as the primary term.

$102 = 100 + 2$

Therefore, the expression can be rewritten as:

$(102)^3 = (100 + 2)^3$

Step 2: Application of the Cubic Identity

[Per the standard binomial expansion for cubes], the relevant algebraic identity is:

$(a + b)^3 = a^3 + b^3 + 3ab(a + b)$

Alternatively, the fully expanded form of this identity is:

$(a + b)^3 = a^3 + 3a^2b + 3ab^2 + b^3$

By mapping our decomposed values to the variables in the identity, we establish:

  • $a = 100$
  • $b = 2$

Step 3: Substitution and Expansion

Substituting $a = 100$ and $b = 2$ into the factored form of the identity yields:

$(100 + 2)^3 = (100)^3 + (2)^3 + 3(100)(2)(100 + 2)$

Step 4: Computation of Individual Terms

We now calculate each term systematically, adhering to the order of operations:

  • Cube of the first term: $(100)^3 = 100 \times 100 \times 100 = 1,000,000$
  • Cube of the second term: $(2)^3 = 2 \times 2 \times 2 = 8$
  • Product of the variables: $3ab = 3(100)(2) = 600$
  • Multiplication of the product term with the binomial sum: $600(100 + 2) = 600(102) = 61,200$

Note: The final term can also be computed via distribution: $600(100) + 600(2) = 60,000 + 1,200 = 61,200$.

Algebraic Expansion Tree of (100 + 2)³ (100 + 2)³ 100³ 3(100²)(2) 3(100)(2²) 1,000,000 60,000 1,200 8 Sum = 1,061,208

Step 5: Final Summation

We combine the computed values to find the final result:

$1,000,000 + 8 + 61,200$

Aligning the values for addition:

$\phantom{+}1,000,000$
$\phantom{+00}61,200$
$\underline{+\phantom{000000}8}$
$\phantom{+}1,061,208$

Final Solution: The evaluated value of $(102)^3$ is 1,061,208.


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