An easy equation.

Algebra Level 4

Solve the equation x ( 3 x 2 19 ) = 2 ( x 2 11 ) x(3x^{2}-19)=2(x^{2}-11) . If the roots of the equation are in the form of a a , r ± m k \frac{r\pm\sqrt{m}}{k} . Find the value of a + r + m + k a+r+m+k .

Note that while expressing your answer in the form given above to get the values of the four variables, the fraction must be in the simplest form (terms)


The answer is 40.

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1 solution

Kartik Sharma
Aug 17, 2014

x ( 3 x 2 19 ) = 2 ( x 2 11 ) x(3{x}^{2} -19) = 2({x}^{2} - 11)

3 x 3 2 x 2 19 x + 22 = 0 = f ( x ) 3{x}^{3} -2{x}^{2} - 19x + 22 = 0 = f(x)

Now, we know one of the roots is in the form of a a , hence we will first find the value of this root. For doing this, we will use the factor-remainder theorem to check what number will be the root of this equation.

After checking by hit-and-trial,

x = 2 is a root of the equation because

3 2 3 2 2 2 19 2 + 22 3*{2}^{3} - 2*{2}^{2} - 19*2 + 22

24 - 8 - 38 + 22 = 0 0

So, a = 2

As,

f(x) = (x - a)(x - r + m k \frac{r + \sqrt{m}}{k} )(x - r m k \frac{r-\sqrt{m}}{k} )

Therefore, (x - r + m k \frac{r + \sqrt{m}}{k} )(x - r m k \frac{r-\sqrt{m}}{k} ) = f(x)/(x-2)

= 3 x 2 + 4 x 11 3{x}^{2} + 4x -11

Now, we will find the roots of this quadratic equation.

Hence, α \alpha , β \beta = 4 ± 4 2 4 3 11 2 3 \frac {-4 \pm \sqrt{ {-4}^{2} - 4* 3* -11}}{2*3}

= 4 ± 148 6 \frac{-4 \pm \sqrt{148}}{6}

= 2 ± 37 3 \frac{ -2 \pm \sqrt{37}}{3}

Therefore, a + r + m + k =2 +(-2) + 37 + 3 = 40 \boxed{40}

It was easy but I am sorry if I made it look messy! ;)

Kartik Sharma - 6 years, 9 months ago

For those who previously got this wrong, I have updated the answer to 40.

Calvin Lin Staff - 6 years, 9 months ago

what did u guys do in the step of 3 2cube -2 2square -19*2+22 i didnt have the feature of the notation thats why i wrote it like this for more clearance it was step 2

maryam khan - 6 years, 8 months ago

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