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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 PDF (31-Jan-2021) (Shift 1)
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 $\frac{(a^2+b^2+c^2)^2}{a^2b^2+b^2c^2+c^2a^2}$

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Important Questions from Identities

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

  2. \(\dfrac{(5.17-2.19)^2-(5.17+2.19)^2}{11.3223}\)
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