Solve equation for value of x: Announcing the arrival of Valued Associate #679: Cesar Manara ...

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Solve equation for value of x:



Announcing the arrival of Valued Associate #679: Cesar Manara
Planned maintenance scheduled April 23, 2019 at 23:30 UTC (7:30pm US/Eastern)Interpret a linear scale as a logarithmic scaleHow to solve logarithm word problem given the exponential equation?How to solve this equation algebraically?What went wrong in these solutions of $log big(x^{log x}big)=4$Trouble solving for exponents with constantsWhat is the value of $x$ in this equation using logarithmsWhat is solution of this logarithmic equationThe solution of the equation $7^{x+7} =8^x$ can be expressed in form $x=log7^7$ to the base $b$. What is $b$?how to solve the logarithmic equation which has both n and lognSolve the equation for x:












5












$begingroup$


Question is to solve the equation for value of $x$.




$$9^{1+log x} - 3^{1+log x} - 210 = 0; quad text{where base of log is }3$$




The answer given is $x=5$



I've tried to solve it. And got two values of $x= -14/3$ and $x=5$. What I've done wrong?



[enter image description here]










share|cite|improve this question









New contributor




Piyush Raj is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
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$endgroup$












  • $begingroup$
    Use $a^{log_b(x)} = x^{log_b(a)}$.
    $endgroup$
    – Viktor Glombik
    35 mins ago










  • $begingroup$
    The final step should be $(3k+14)(k-5)=0$ (multiplication since you are factoring) This is what then allows you to reach your conclusion.
    $endgroup$
    – John Doe
    33 mins ago


















5












$begingroup$


Question is to solve the equation for value of $x$.




$$9^{1+log x} - 3^{1+log x} - 210 = 0; quad text{where base of log is }3$$




The answer given is $x=5$



I've tried to solve it. And got two values of $x= -14/3$ and $x=5$. What I've done wrong?



[enter image description here]










share|cite|improve this question









New contributor




Piyush Raj is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.







$endgroup$












  • $begingroup$
    Use $a^{log_b(x)} = x^{log_b(a)}$.
    $endgroup$
    – Viktor Glombik
    35 mins ago










  • $begingroup$
    The final step should be $(3k+14)(k-5)=0$ (multiplication since you are factoring) This is what then allows you to reach your conclusion.
    $endgroup$
    – John Doe
    33 mins ago
















5












5








5





$begingroup$


Question is to solve the equation for value of $x$.




$$9^{1+log x} - 3^{1+log x} - 210 = 0; quad text{where base of log is }3$$




The answer given is $x=5$



I've tried to solve it. And got two values of $x= -14/3$ and $x=5$. What I've done wrong?



[enter image description here]










share|cite|improve this question









New contributor




Piyush Raj is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.







$endgroup$




Question is to solve the equation for value of $x$.




$$9^{1+log x} - 3^{1+log x} - 210 = 0; quad text{where base of log is }3$$




The answer given is $x=5$



I've tried to solve it. And got two values of $x= -14/3$ and $x=5$. What I've done wrong?



[enter image description here]







logarithms






share|cite|improve this question









New contributor




Piyush Raj is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.











share|cite|improve this question









New contributor




Piyush Raj is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.









share|cite|improve this question




share|cite|improve this question








edited 38 mins ago









John Doe

12.1k11340




12.1k11340






New contributor




Piyush Raj is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.









asked 43 mins ago









Piyush RajPiyush Raj

304




304




New contributor




Piyush Raj is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.





New contributor





Piyush Raj is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.






Piyush Raj is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.












  • $begingroup$
    Use $a^{log_b(x)} = x^{log_b(a)}$.
    $endgroup$
    – Viktor Glombik
    35 mins ago










  • $begingroup$
    The final step should be $(3k+14)(k-5)=0$ (multiplication since you are factoring) This is what then allows you to reach your conclusion.
    $endgroup$
    – John Doe
    33 mins ago




















  • $begingroup$
    Use $a^{log_b(x)} = x^{log_b(a)}$.
    $endgroup$
    – Viktor Glombik
    35 mins ago










  • $begingroup$
    The final step should be $(3k+14)(k-5)=0$ (multiplication since you are factoring) This is what then allows you to reach your conclusion.
    $endgroup$
    – John Doe
    33 mins ago


















$begingroup$
Use $a^{log_b(x)} = x^{log_b(a)}$.
$endgroup$
– Viktor Glombik
35 mins ago




$begingroup$
Use $a^{log_b(x)} = x^{log_b(a)}$.
$endgroup$
– Viktor Glombik
35 mins ago












$begingroup$
The final step should be $(3k+14)(k-5)=0$ (multiplication since you are factoring) This is what then allows you to reach your conclusion.
$endgroup$
– John Doe
33 mins ago






$begingroup$
The final step should be $(3k+14)(k-5)=0$ (multiplication since you are factoring) This is what then allows you to reach your conclusion.
$endgroup$
– John Doe
33 mins ago












1 Answer
1






active

oldest

votes


















4












$begingroup$

You have solved correctly just made one error towards the end.
Note that the domain of $log(x)$ is $x > 0$ so $x=-14/3$ is rejected as it is not in the domain of the function.






share|cite|improve this answer











$endgroup$









  • 2




    $begingroup$
    Yep. And going from $(3 x + 14) + (x - 5) = 0$ does not mean that either term in the sum is $0$.
    $endgroup$
    – David G. Stork
    34 mins ago










  • $begingroup$
    He meant$(3x+14)(x-5) = 0$. He was solving a quadratic. Must be $times$ in the middle.
    $endgroup$
    – Vizag
    32 mins ago












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1 Answer
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active

oldest

votes








1 Answer
1






active

oldest

votes









active

oldest

votes






active

oldest

votes









4












$begingroup$

You have solved correctly just made one error towards the end.
Note that the domain of $log(x)$ is $x > 0$ so $x=-14/3$ is rejected as it is not in the domain of the function.






share|cite|improve this answer











$endgroup$









  • 2




    $begingroup$
    Yep. And going from $(3 x + 14) + (x - 5) = 0$ does not mean that either term in the sum is $0$.
    $endgroup$
    – David G. Stork
    34 mins ago










  • $begingroup$
    He meant$(3x+14)(x-5) = 0$. He was solving a quadratic. Must be $times$ in the middle.
    $endgroup$
    – Vizag
    32 mins ago
















4












$begingroup$

You have solved correctly just made one error towards the end.
Note that the domain of $log(x)$ is $x > 0$ so $x=-14/3$ is rejected as it is not in the domain of the function.






share|cite|improve this answer











$endgroup$









  • 2




    $begingroup$
    Yep. And going from $(3 x + 14) + (x - 5) = 0$ does not mean that either term in the sum is $0$.
    $endgroup$
    – David G. Stork
    34 mins ago










  • $begingroup$
    He meant$(3x+14)(x-5) = 0$. He was solving a quadratic. Must be $times$ in the middle.
    $endgroup$
    – Vizag
    32 mins ago














4












4








4





$begingroup$

You have solved correctly just made one error towards the end.
Note that the domain of $log(x)$ is $x > 0$ so $x=-14/3$ is rejected as it is not in the domain of the function.






share|cite|improve this answer











$endgroup$



You have solved correctly just made one error towards the end.
Note that the domain of $log(x)$ is $x > 0$ so $x=-14/3$ is rejected as it is not in the domain of the function.







share|cite|improve this answer














share|cite|improve this answer



share|cite|improve this answer








edited 36 mins ago









DMcMor

2,91321328




2,91321328










answered 37 mins ago









VizagVizag

514112




514112








  • 2




    $begingroup$
    Yep. And going from $(3 x + 14) + (x - 5) = 0$ does not mean that either term in the sum is $0$.
    $endgroup$
    – David G. Stork
    34 mins ago










  • $begingroup$
    He meant$(3x+14)(x-5) = 0$. He was solving a quadratic. Must be $times$ in the middle.
    $endgroup$
    – Vizag
    32 mins ago














  • 2




    $begingroup$
    Yep. And going from $(3 x + 14) + (x - 5) = 0$ does not mean that either term in the sum is $0$.
    $endgroup$
    – David G. Stork
    34 mins ago










  • $begingroup$
    He meant$(3x+14)(x-5) = 0$. He was solving a quadratic. Must be $times$ in the middle.
    $endgroup$
    – Vizag
    32 mins ago








2




2




$begingroup$
Yep. And going from $(3 x + 14) + (x - 5) = 0$ does not mean that either term in the sum is $0$.
$endgroup$
– David G. Stork
34 mins ago




$begingroup$
Yep. And going from $(3 x + 14) + (x - 5) = 0$ does not mean that either term in the sum is $0$.
$endgroup$
– David G. Stork
34 mins ago












$begingroup$
He meant$(3x+14)(x-5) = 0$. He was solving a quadratic. Must be $times$ in the middle.
$endgroup$
– Vizag
32 mins ago




$begingroup$
He meant$(3x+14)(x-5) = 0$. He was solving a quadratic. Must be $times$ in the middle.
$endgroup$
– Vizag
32 mins ago










Piyush Raj is a new contributor. Be nice, and check out our Code of Conduct.










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