What is the solution to log5(10x-1)=log5(9x=7)

1 answer:

4 0

$Domain:\\\\10x-1 > 0\ and\ 9x+7 > 0\\\\10x > 1\ and\ 9x > -7\\\\x > \dfrac{1}{10}\ and\ x > -\dfrac{7}{9}\Rightarrow x > \dfrac{1}{10}\\\\D=\left\{x|x > \dfrac{1}{10}\right\}\\\\\log_5(10x-1)=\log_5(9x+7)\iff10x-1=9x+7\qquad\text{add 1 to both sides}\\\\10x=9x+8\qquad\text{subtract 9x from both sides}\\\\x=8\in D\\\\Answer:\ \boxed{x=8}$

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Three friends met for a book club at a coffee shop, each friend ordered a cup of coffee and two donuts. the total of the order w

4vir4ik [10]

Answer:

$Cost\ of\ donut=\frac{49}{24}\approx \$2.042\\\\cost\ of\ donuts=\frac{49}{4}\approx \$12.25$

Step-by-step explanation:

$Let\ cost\ of\ coffee=y\\\\cost\ of\ one\ donut=x\\\\Each\ friend\ buy\ one\ coffee\ and\ two\ donuts\\\\Amount\ for\ 1\ friend=Cost\ of\ coffee+2\times cost\ of\ donut\\\\Amount\ for\ 1\ friend=y+2x\\\\Amount\ required\ for\ 3\ friend=3\times Amount\ for\ 1\ friend\\\\Amount\ required\ for\ 3\ friend=3\times (y+2x)\\\\Amount\ required\ for\ 3\ friend=3y+6x\\\\Total\ bill=\$ 22\\\\3y+2x=22\\\\Given\ cost\ of\ coffee=\$3.25\\\\y=\$3.25$

$Hence\ solution\ of\ following\ system\ of\ equation\ will\ give\ cost\ of\ donut:\\\\3y+6x=22\\\\y=3.25\\\\\\Substitute\ y=3.25\ in\ first\ equation\\\\3\times 3.25+6x=22\\\\9.75+6x=22\\\\6x=22-9.75\\\\6x=12.25\\\\x=\frac{12.25}{6}\\\\x=\frac{49}{24}\approx \$2.042\\\\Cost\ of\ donut=\frac{49}{24}\approx \$2.042$

See attached diagram.

$Each\ friend\ takes\ 2\ donuts\\\\Total\ donuts=Number\ of\ friends\times 2\\\\Total\ donuts=3\times 2=6\\\\cost\ of\ donuts=number\ of\ donuts\times cost\ of\ 1\ donut\\\\cost\ of\ donuts=6\times \frac{49}{24}\\\\cost\ of\ donuts=\frac{49}{4}\approx \$12.25$