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If $a + b + c = 17$, $abc = 168$, and $ab + bc + ca = 94$, then $a^3 + b^3 + c^3 = ?$

This question was previously asked in
RRB NTPC 2019 CBT 1 Question Paper (8-Mar-2021) (Shift 2)
The correct answer is
623

The problem asks for the value of $a^3 + b^3 + c^3$ given the values of $a+b+c$, $abc$, and $ab+bc+ca$. We can solve this using algebraic identities.

Sum of Cubes Calculation

We use the identity:

$a^3 + b^3 + c^3 - 3abc = (a+b+c)(a^2+b^2+c^2 - ab - bc - ca)$

First, we need to find the value of $a^2+b^2+c^2$. We use the identity:

$(a+b+c)^2 = a^2+b^2+c^2 + 2(ab+bc+ca)$

Substitute the given values:

$a+b+c = 17$ $ab+bc+ca = 94$

So, the equation becomes:

$17^2 = a^2+b^2+c^2 + 2(94)$ $289 = a^2+b^2+c^2 + 188$

Now, solve for $a^2+b^2+c^2$:

$a^2+b^2+c^2 = 289 - 188$ $a^2+b^2+c^2 = 101$

Calculating $a^3 + b^3 + c^3$

Now substitute the known values into the sum of cubes identity:

$a^3 + b^3 + c^3 - 3abc = (a+b+c)(a^2+b^2+c^2 - (ab+bc+ca))$

Given values:

$a+b+c = 17$ $abc = 168$ $a^2+b^2+c^2 = 101$ $ab+bc+ca = 94$

Substitute these values into the identity:

$a^3 + b^3 + c^3 - 3(168) = (17)(101 - 94)$ $a^3 + b^3 + c^3 - 504 = (17)(7)$ $a^3 + b^3 + c^3 - 504 = 119$

Finally, solve for $a^3 + b^3 + c^3$:

$a^3 + b^3 + c^3 = 119 + 504$ $a^3 + b^3 + c^3 = 623$
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Similar Questions

  1. If $a + b + c = 10$ and $ab + bc + ca = 31$, find the value of $a^2 + b^2 + c^2$
  2. If $a + b + c = 0$, then find the value of $\frac{(a^2+b^2+c^2)^2}{a^2b^2+b^2c^2+c^2a^2}$

  3. If $x^4 + \frac{1}{x^4} = 322$, then $x^3 - \frac{1}{x^3} = ?$
  4. If $(x + \frac{1}{x}) = 7$, then $(x - \frac{1}{x})$ is equal to:
  5. If $x + y + z = 0$, then the value of $\frac{x^2}{yz} + \frac{y^2}{zx} + \frac{z^2}{xy}$ is:
  6. What is the value of the following expression:

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  7. If $a = \frac{b^2}{b - a}$, then the value of $a^3 + b^3$ is:
  8. If $ab = 10$ and $a^{2} + b^{2} = 29$, then $(a - b)^{2} = ?$
  9. Find the value of $\frac{(74 + 47)^2 + (74 - 47)^2}{74^2 + 47^2}$
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Important Questions from Identities

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

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

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