You don't need to find all the values

Algebra Level 2

10 0 x 2 6 x + 1 + 5 = 10 \large 100^{x^2-6x+1} + 5 = 10

Find the sum of all the roots that satisfy the equation above.


The answer is 6.

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3 solutions

Manav D.S.R
Mar 20, 2016

The solution to this problem is:

Step 1: 10 0 x 2 6 x + 1 + 5 = 10 100^{x^2-6x+1}+5=10

Step 2: 10 0 x 2 6 x + 1 = 10 5 100^{x^2-6x+1}=10-5

Step 3: 10 0 x 2 6 x + 1 = 5 100^{x^2-6x+1}=5

Step 4: ln ( 10 0 x 2 6 x + 1 ) = ln ( 5 ) \ln(100^{x^2-6x+1})=\ln(5)

Step 5: ( x 2 6 x + 1 ) × ln ( 100 ) = ln ( 5 ) (x^2-6x+1)\times\ln(100)=\ln(5)

Step 6: x 2 6 x + 1 = ln ( 5 ) ln ( 100 ) \displaystyle x^2-6x+1=\frac{\ln(5)}{\ln(100)}

Step 7: Solve the quadratic equation to find the values of x x which will be: x = 5.88954754282 x=5.88954754282 and x = 0.110452457185 x=0.110452457185

Step 8: Add 5.88954754282 5.88954754282 and 0.110452457185 0.110452457185

Step 9: The answer will be 6 6

WRITE THESE STEPS IF YOU GOT WRONG TO HAVE A CLEARER UNDERSTANDING.

THANK YOU.

Great job,here's a tip!.At last we get an equation 2 x 2 12 x + log 2 + 1 = 0. 2x^2-12x+\log2+1=0. Then we can simply use Vieta's to get the sum of root as 12 2 = 6 -\dfrac{-12}{2}=\boxed{6} . Also,you can make your solutions more attractive and easy to understand with LaTeX \LaTeX .See this .

Rohit Udaiwal - 5 years, 2 months ago

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Ok, Thanks for the information.

Manav D.S.R - 5 years, 2 months ago
Hung Woei Neoh
Jun 1, 2016

10 0 x 2 6 x + 1 + 5 = 10 10 0 x 2 6 x + 1 = 5 log 10 ( 1 0 2 ) x 2 6 x + 1 = log 10 5 2 ( x 2 6 x + 1 ) = log 10 5 x 2 6 x + 1 = log 10 5 2 x 2 6 x + 1 log 10 5 2 = 0 100^{x^2-6x+1} +5 = 10\\ 100^{x^2-6x+1} = 5\\ \log_{10}(10^2)^{x^2-6x+1} = \log_{10} 5\\ 2(x^2-6x+1) = \log_{10} 5\\ x^2 - 6x + 1 = \dfrac{\log_{10} 5}{2}\\ x^2 - 6x + 1 - \dfrac{\log_{10} 5}{2} = 0

Given that x 2 ( Sum of roots ) x + ( Product of roots ) = 0 x^2 - (\text{Sum of roots})x + (\text{Product of roots}) = 0

Sum of roots = 6 \boxed{6}

Kay Xspre
Mar 20, 2016

10 0 x 2 6 x + 1 = 5 100^{x^2-6x+1} = 5 , which, when take log 100, gives x 2 6 x + 1 = log 5 x^2-6x+1 = \log \sqrt{5} , or simply ( x 3 ) 2 = 8 + log 5 (x-3)^2 = 8+\log \sqrt{5} Hence, x = 3 ± 8 + log 5 x = 3\pm\sqrt{8+\log \sqrt{5}} , and their sum is 6.

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