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If (s − a) + (s − b) + (s − c) = s, then the value of \(\rm\frac{(s−a)^2+(s−b)^2+(s−c)^2+s^2}{a^2+b^2+c^2}\)  will be

This question was previously asked in
CDS I 2016 English Previous Year Paper (14-Feb-2016)
The correct answer is

1

Understanding the Algebraic Problem

The problem provides us with an equation involving the variables \(s\), \(a\), \(b\), and \(c\), and asks us to find the value of a specific algebraic expression involving the same variables. The given equation is \((s - a) + (s - b) + (s - c) = s\). The expression whose value we need to determine is \(\rm\frac{(s−a)^2+(s−b)^2+(s−c)^2+s^2}{a^2+b^2+c^2}\).

Simplifying the Given Equation

Let's start by simplifying the given equation:

\(\qquad (s - a) + (s - b) + (s - c) = s\)

Combine the terms on the left side:

\(\qquad s - a + s - b + s - c = s\)

\(\qquad 3s - (a + b + c) = s\)

Now, isolate the term involving \(a, b, c\) and \(s\):

\(\qquad 3s - s = a + b + c\)

\(\qquad 2s = a + b + c\)

This relationship, \(a+b+c = 2s\), is key to solving the problem.

Evaluating the Algebraic Expression

We need to find the value of the expression: \(\rm\frac{(s−a)^2+(s−b)^2+(s−c)^2+s^2}{a^2+b^2+c^2}\).

Let's focus on the numerator first: \((s−a)^2+(s−b)^2+(s−c)^2+s^2\).

Expand the squared terms using the algebraic identity \((x-y)^2 = x^2 - 2xy + y^2\):

  • \((s-a)^2 = s^2 - 2as + a^2\)
  • \((s-b)^2 = s^2 - 2bs + b^2\)
  • \((s-c)^2 = s^2 - 2cs + c^2\)

Now, let's sum these three expanded terms:

\((s-a)^2 + (s-b)^2 + (s-c)^2 = (s^2 - 2as + a^2) + (s^2 - 2bs + b^2) + (s^2 - 2cs + c^2)\)

Group the terms:

\(= (s^2 + s^2 + s^2) - (2as + 2bs + 2cs) + (a^2 + b^2 + c^2)\)

\(= 3s^2 - 2s(a + b + c) + (a^2 + b^2 + c^2)\)

From our simplified equation, we know that \(a+b+c = 2s\). Substitute this into the expression:

\(= 3s^2 - 2s(2s) + (a^2 + b^2 + c^2)\)

\(= 3s^2 - 4s^2 + a^2 + b^2 + c^2\)

\(= -s^2 + a^2 + b^2 + c^2\)

Now, we need to add the remaining \(s^2\) term from the original numerator expression:

Numerator \(= (s-a)^2+(s-b)^2+(s-c)^2+s^2\)

Numerator \(= (-s^2 + a^2 + b^2 + c^2) + s^2\)

Numerator \(= a^2 + b^2 + c^2\)

So, the expression we need to evaluate becomes:

\(\rm\frac{a^2+b^2+c^2}{a^2+b^2+c^2}\)

Assuming that \(a^2+b^2+c^2 \neq 0\), the value of this expression simplifies to 1.

If \(a^2+b^2+c^2 = 0\), then since \(a, b, c\) are typically real numbers in such problems, this would imply \(a=0, b=0, c=0\). Substituting these into the original equation \((s-a)+(s-b)+(s-c)=s\) gives \((s-0)+(s-0)+(s-0)=s\), which is \(3s=s\), implying \(2s=0\), so \(s=0\). In this specific case (\(a=b=c=s=0\)), the expression becomes \(0/0\), which is indeterminate. However, since numerical options are provided, we assume a scenario where the denominator is not zero, leading to a definite value.

Conclusion on the Value of the Expression

Based on the simplification of the given equation and the algebraic expression, the value is found to be 1.

Step Calculation/Reasoning
1 Simplify the given equation: \((s-a)+(s-b)+(s-c)=s \implies 3s-(a+b+c)=s \implies a+b+c=2s\)
2 Expand the squared terms in the numerator: \((s-a)^2+(s-b)^2+(s-c)^2 = (s^2-2as+a^2) + (s^2-2bs+b^2) + (s^2-2cs+c^2)\)
3 Group terms: \(= 3s^2 - 2s(a+b+c) + (a^2+b^2+c^2)\)
4 Substitute \(a+b+c=2s\): \(= 3s^2 - 2s(2s) + (a^2+b^2+c^2) = 3s^2 - 4s^2 + a^2+b^2+c^2 = -s^2 + a^2+b^2+c^2\)
5 Add the remaining \(s^2\) to the numerator: \((-s^2 + a^2+b^2+c^2) + s^2 = a^2+b^2+c^2\)
6 Form the final expression: \(\rm\frac{a^2+b^2+c^2}{a^2+b^2+c^2}\)
7 Simplify (assuming denominator \(\neq 0\)): \(= 1\)

Revision Table: Algebraic Simplification

Reviewing the key steps involved in simplifying algebraic expressions and equations:

  • Always start by simplifying any given equations to establish relationships between variables.
  • Expand squared or higher power terms carefully using appropriate algebraic identities.
  • Collect like terms.
  • Substitute known relationships between variables to simplify expressions further.
  • Pay attention to potential cases where denominators might be zero, although often the context of multiple-choice options implies a non-zero denominator and a specific value.

Additional Information: Related Algebraic Concepts

This problem involves basic algebraic manipulation. Here are some related concepts:

  • Algebraic Equations: Statements where two algebraic expressions are equal, used to find unknown values or relationships between variables.
  • Algebraic Expressions: Combinations of variables, constants, and algebraic operations (addition, subtraction, multiplication, division, exponentiation).
  • Identities: Equations that are true for all possible values of the variables involved (e.g., \((x-y)^2 = x^2 - 2xy + y^2\)).
  • Substitution: Replacing a variable or expression with another equivalent variable or expression to simplify an equation or expression.
  • Semi-perimeter: In geometry, if \(a, b, c\) are side lengths of a triangle, \(s = (a+b+c)/2\) is the semi-perimeter, leading to the relationship \(a+b+c=2s\). While the problem doesn't explicitly state it's a triangle, the relationship \(a+b+c=2s\) derived from the given equation is consistent with this concept.
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Important Questions from Identities

  1. Simplify.

    \(\frac{2.5 \times 2.5 \times 2.5-1.5 \times 1.5 \times 1.5}{2.5 \times 2.5+2.5 \times 1.5+1.5 \times 1.5}\)

  2. If \(2x + { {1} \over 3x}= 5, x ≠ 0\) , then what is the value of  \(27x^3+{{1} \over 8x^3}\) ?

  3. If x 2 + 4y 2 = 40, xy = 6 and x > 2y then the value of x - 2y is:

  4. \(\dfrac{(0.73)^3+(0.31)^3}{(0.73)^2-0.73\times0.31+(0.31)^2}\)
  5. \(\dfrac{(5.17-2.19)^2-(5.17+2.19)^2}{11.3223}\)
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