Will the modulus function change it all?

Algebra Level 4

x 3 3 x 2 10 x + 3 = 1 \large |x-3|^{3x^2-10x+3} = 1

Find three times the product of the real values of x x that satisfy the equation above.

Note : 0 0 0^0 is not defined.


The answer is 8.

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7 solutions

Rohit Udaiwal
Oct 26, 2015

case 1 : 3 x 2 10 x + 3 = 0 3x^2-10x+3=0 where x 3 0 |x-3|\ne 0 .

x = 10 ± 100 36 2 × 3 x = 10 ± 8 6 x = 18 6 , 2 6 = 3 , 1 3 . \implies x=\dfrac {10 \pm \sqrt {100-36}}{2×3}\implies x=\dfrac {10 \pm 8}{6}\implies x=\frac{18}{6},\frac {2 }{6}=3,\dfrac {1}{3}.

But x 3 = 0 |x-3|=0 when x = 3 x=3 x = 1 3 \therefore x=\dfrac {1}{3} .

case 2 : x 3 = 1 |x-3|=1 where 3 x 2 10 x + 3 3x^{2}-10x+3 is any number.

x 3 = 1 x 3 = ± 1 x = 2 , 4 x = 2 , 4. |x-3|=1 \implies x-3=\pm 1 \implies x=2,4 \therefore x=2,4.

case 3 : x 3 = 1 |x-3|=-1 where 3 x 2 10 x + 3 3x^{2}-10x+3 is an even number.

But A 0 x 3 1. |A|\ge 0 \implies |x-3|\ne -1.

x = 1 3 , 2 , 4 \therefore x=\dfrac {1}{3},2,4

3 × 1 3 × 2 × 4 = 8 . \therefore 3×\dfrac {1}{3}×2×4=\boxed{8}.

note that any e i z + 3 e^{iz}+3 satisfies this for real z. the question must mention real x!

Aareyan Manzoor - 5 years, 7 months ago

Log in to reply

Thanks ,I've edited it.

Rohit Udaiwal - 5 years, 7 months ago

I missed 1 3 \frac13

Arulx Z - 5 years, 7 months ago

Oh I multiply each root by 3

Asif Mujawar - 5 years, 7 months ago

Comprehensive solution.

Abhishek Sharma - 5 years, 7 months ago
Vipul Sharma
Nov 1, 2015

Take log on both sides

At first we need x 3 = 1 |x-3|=1 and is easy to see that two of the solutions are 2 2 and 4 4 . Now we don't want the expression to become 0 0 0^{0} so we look for y y such that y 3 = 0 |y-3|=0 , so y = 3 y=3 , we evaluate in the exponent 3 3 2 10 3 + 3 = 0 3\cdot 3^{2}-10\cdot 3+3=0 . So 3 3 is solution of the exponent and x 3 x\ne 3 . As the product of solutions of the exponent is 3 3 = 1 \frac{3}{3}=1 and one of the solutions is 3 3 , the other is 1 3 \frac{1}{3} . So 3 × 2 4 3 = 2 4 = 8 3 \times \frac{2\cdot 4}{3}=2\cdot 4=8 . An easier way to do it by only mind, I think. Great problem!

Lukas Leibfried
Oct 31, 2015

The expression can be equal to 1 if and only if x 3 = 1 \left| x-3 \right| =1 or 3 x 2 10 x + 3 = 0 3{ x }^{ 2 }-10x+3=0 and x 3 0 \left| x-3 \right| \neq 0 .

x 3 = 1 \left| x-3 \right| =1 for x = 4 x = 4 and x = 2 x = 2 .

By factoring 3 x 2 10 x + 3 = 0 3{ x }^{ 2 }-10x+3=0 , we find that 3 ( x 1 3 ) ( x 3 ) = 0 3(x-\frac { 1 }{ 3 } )(x-3)=0 , therefore our possible solutions are x = 1 3 x = \frac{1}{3} and x = 3 x = 3 . However, the latter solution does not satisfy the condition x 3 0 \left| x-3 \right| \neq 0 , therefore our values of x x are 4, 2, and 1 3 \frac{1}{3} .

( 4 × 2 × 1 3 ) × 3 = 8 (4 \times 2 \times \frac{1}{3}) \times 3 = \boxed{8}

Patrick Bourg
Oct 31, 2015

Suppose x 3 x \neq 3 solves the equation. Raise both sides to the power 1 x 3 \frac{1}{x-3} to obtain : x 3 3 x 1 = 1. |x-3|^{3x-1} = 1. Now, if x = 1 3 x=\frac{1}{3} , we see that the equation is satisfied. So, this is one solution. Assume, now that x 1 3 x \neq \frac{1}{3} . By a similar process as before, we can raise to the appropriate power to get x 3 = 1 , |x-3|=1, which is found to have solutions : 2 and 4. We can then easily check that these solutions satisfy our equation.

Thus, collecting everything together, we have 3 solutions : 1 3 , 2 , 4 \frac{1}{3}, 2, 4 . Hence the answer is 8, as required.

Atul Shivam
Oct 28, 2015

We got three values of x x say 2 , 4 1 3 2,4\frac{1}{3} Simply multiply them 3 ( 2 × 4 × 1 3 ) 3(2×4×\frac{1}{3}) which is 8 \boxed{8}

Sai Aryanreddy
Oct 28, 2015

lol very easy i dont know who rated it as level 4!!!!!!!!. i am of level 2 in algebra THE SOLUTION FOR THIS PROBLEM IS

ROOTS OF THE EQUATION 3X2-1OX+3=0 are 0.33333..... and 3.SO IF THE POWER IS 0 THEN RESULTANT GIVES 1.BUT,0 POWER 0 IS NOT DEFINED SO 3 DOESNT SATISFY. BUT IF THE BASE IS 1 WHAT EVER MAY BE THE POWER RESULTANT WILL BE 1. SO WE HAVE TWO CASES, 1 IS X=4. CASE 2 IS X= 2 SO ANS IS 3 x 2 x 4 x 0.333333....=4 x 2 x 1=8

Different things are easier or harder for different people. There are some level five problems which I have no problem solving and others where I don't even know how to start.

Lukas Leibfried - 5 years, 7 months ago

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