How do you solve log_3x=log_9 7x-6log3x=log97x6?

1 Answer
Mar 21, 2016

x=7/531441x=7531441

Explanation:

11. Start by moving all logs to the left side of the equation.

log_3(x)=log_9(7x)-6log3(x)=log9(7x)6

log_3(x)-log_9(7x)=-6log3(x)log9(7x)=6

22. Use the change of base formula, log_color(blue)n(color(red)m)=(log_color(purple)b(color(red)m))/(log_color(purple)b(color(blue)n))logn(m)=logb(m)logb(n), to rewrite log_9(7x)log9(7x) with a base of 33.

log_3(x)-(log_3(7x))/(log_3(9))=-6log3(x)log3(7x)log3(9)=6

33. Use the log property, log_color(purple)b(color(purple)b^color(orange)x)=color(orange)xlogb(bx)=x, to rewrite log_3(9)log3(9).

log_3(x)-(log_3(7x))/(log_3(3^2))=-6log3(x)log3(7x)log3(32)=6

log_3(x)-(log_3(7x))/2=-6log3(x)log3(7x)2=6

44. Use the log property, log_color(purple)b(color(red)m^color(blue)n)=color(blue)n*log_color(purple)b(color(red)m)logb(mn)=nlogb(m), to rewrite (log_3(7x))/2log3(7x)2.

log_3(x)-1/2(log_3(7x))=-6log3(x)12(log3(7x))=6

log_3(x)-log_3((7x)^(1/2))=-6log3(x)log3((7x)12)=6

55. Use the log property, log_color(purple)b(color(red)m/color(blue)n)=log_color(purple)b(color(red)m)-log_color(purple)b(color(blue)n)logb(mn)=logb(m)logb(n) to simplify the left side of the equation.

log_3(x/((7x)^(1/2)))=-6log3(x(7x)12)=6

log_3(x^(1/2)/7^(1/2))=-6log3(x12712)=6

66. Use the log property, log_color(purple)b(color(purple)b^color(orange)x)=color(orange)xlogb(bx)=x, to rewrite the right side of the equation.

log_3(x^(1/2)/7^(1/2))=-log_3(3^6)log3(x12712)=log3(36)

77. Use the log property, log_color(purple)b(color(red)m^color(blue)n)=color(blue)n*log_color(purple)b(color(red)m)logb(mn)=nlogb(m), to rewrite the right side of the equation.

log_3(x^(1/2)/7^(1/2))=log_3(3^-6)log3(x12712)=log3(36)

88. Since the equation now follows a "log=loglog=log" situation, where the bases are the same on both sides, rewrite the equation without the "loglog" portion.

x^(1/2)/7^(1/2)=3^-6x12712=36

99. Solve for xx.

x^(1/2)/7^(1/2)=1/3^6x12712=136

x^(1/2)/7^(1/2)=1/729x12712=1729

x^(1/2)=7^(1/2)/729x12=712729

(x^(1/2))^2=(7^(1/2)/729)^2(x12)2=(712729)2

color(green)(|bar(ul(color(white)(a/a)x=7/531441color(white)(a/a)|)))