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Question

Find the value of $a^2 + b^2 + c^2 - 2ab + 2ac - 2bc$, if $a = x + y, b = x - y$ and $c = 2x - 1$

This question was previously asked in
RRB NTPC 2019 CBT 1 Question Paper (8-Mar-2021) (Shift 2)
The correct answer is
$(2x + 2y - 1)^2$

Algebraic Identity Identification

The expression $a^2 + b^2 + c^2 - 2ab + 2ac - 2bc$ is recognized as the expansion of a squared trinomial. Specifically, it matches the form $(a - b + c)^2$.

Verification: $(a - b + c)^2 = a^2 + (-b)^2 + c^2 + 2(a)(-b) + 2(a)(c) + 2(-b)(c)$

$= a^2 + b^2 + c^2 - 2ab + 2ac - 2bc$.

Therefore, the given expression is equivalent to $(a - b + c)^2$.

Substitution of Values

Substitute the provided values for $a$, $b$, and $c$ into the equivalent expression $(a - b + c)^2$:

$a = x + y$

$b = x - y$

$c = 2x - 1$

Substituting these into $(a - b + c)^2$ yields: $((x + y) - (x - y) + (2x - 1))^2$

Expression Simplification

Simplify the terms inside the parentheses:

$(x + y) - (x - y) + (2x - 1)$

Distribute the negative sign: $x + y - x + y + 2x - 1$

Combine like terms: $(x - x + 2x) + (y + y) - 1$

$= 2x + 2y - 1$

Final Result Calculation

The simplified expression inside the parentheses is $2x + 2y - 1$. Squaring this result provides the final value:

$(2x + 2y - 1)^2$

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Similar Questions

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Important Questions from Algebra

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