Rules of Logarithms Combined: Resulting in a quadratic equation

Examples with solutions for Rules of Logarithms Combined: Resulting in a quadratic equation

Exercise #1

log7x4log72x2=3 \log_7x^4-\log_72x^2=3

?=x

Video Solution

Step-by-Step Solution

logaxlogay=logaxy \log_ax-\log_ay=\log_a\frac{x}{y}

log7x4log72x2= \log_7x^4-\log_72x^2=

log7x42x2=3 \log_7\frac{x^4}{2x^2}=3

73=x22 7^3=\frac{x^2}{2}

We multiply by: 2 2

273=x2 2\cdot7^3=x^2

Extract the root

x=680=714 x=\sqrt{680}=7\sqrt{14}

x=680=714 x=-\sqrt{680}=-7\sqrt{14}

Answer

714  , 714 -7\sqrt{14\text{ }}\text{ , }7\sqrt{14}

Exercise #2

log7x+log(x+1)log7=log2xlogx \log7x+\log(x+1)-\log7=\log2x-\log x

?=x ?=x

Video Solution

Step-by-Step Solution

Defined domain

x>0

x+1>0

x>-1

log7x+log(x+1)log7=log2xlogx \log7x+\log\left(x+1\right)-\log7=\log2x-\log x

log7x(x+1)7=log2xx \log\frac{7x\cdot\left(x+1\right)}{7}=\log\frac{2x}{x}

We reduce by: 7 7 and by X X

x(x+1)=2 x\left(x+1\right)=2

x2+x2=0 x^2+x-2=0

(x+2)(x1)=0 \left(x+2\right)\left(x-1\right)=0

x+2=0 x+2=0

x=2 x=-2

Undefined domain x>0

x1=0 x-1=0

x=1 x=1

Defined domain

Answer

1 1

Exercise #3

Solve for X:

log3(x+2)log29=4 \log_3(x+2)\cdot\log_29=4

Video Solution

Answer

2 2

Exercise #4

log2x+log2x2=5 \log_2x+\log_2\frac{x}{2}=5

?=x

Video Solution

Answer

8 8

Exercise #5

log4x2log716=2log78 \log_4x^2\cdot\log_716=2\log_78

?=x

Video Solution

Answer

±8 \pm\sqrt{8}

Exercise #6

log2(x2+3x+3)log314=2log3(4x+22) \log_2(x^2+3x+3)\cdot\log_3\frac{1}{4}=-2\log_3(\frac{4x+2}{-2})

?=x

Video Solution

Answer

1,4 -1,-4

Exercise #7

Find X

log84x+log8(x+2)log83=3 \frac{\log_84x+\log_8(x+2)}{\log_83}=3

Video Solution

Answer

1+312 -1+\frac{\sqrt{31}}{2}

Exercise #8

log3x+log(x1)=3 \log3x+\log(x-1)=3

?=x ?=x

Video Solution

Answer

18.8 18.8

Exercise #9

log4x+log4(x+2)=2 \log_4x+\log_4(x+2)=2

Video Solution

Answer

1+17 -1+\sqrt{17}

Exercise #10

log27log48log3x2=log24log47log38 \log_27\cdot\log_48\cdot\log_3x^2=\log_24\cdot\log_47\cdot\log_38

?=x

Video Solution

Answer

2,2 -2,2

Exercise #11

log7×lnx=ln7log(x2+8x8) \log7\times\ln x=\ln7\cdot\log(x^2+8x-8)

?=x

Video Solution

Answer

1 1

Exercise #12

2log(x+1)=log(2x2+8x) 2\log(x+1)=\log(2x^2+8x)

x=? x=\text{?}

Video Solution

Answer

3+10 -3+\sqrt{10}

Exercise #13

Calculate X:

2log(x+4)=1 2\log(x+4)=1

Video Solution

Answer

4+10 -4+\sqrt{10}

Exercise #14

log4(x2+8x+1)log48=2 \frac{\log_4(x^2+8x+1)}{\log_48}=2

x=? x=\text{?}

Video Solution

Answer

4±79 -4\pm\sqrt{79}

Exercise #15

ln(4x+3)ln(x28)=2 \ln(4x+3)-\ln(x^2-8)=2

?=x

Video Solution

Answer

3.18 3.18

Exercise #16

?=a

ln(a+5)+ln(a+7)=0 \ln(a+5)+\ln(a+7)=0

Video Solution

Answer

6+2 -6+\sqrt{2}

Exercise #17

2log7(x+1)log7e=ln(3x2+1) \frac{2\log_7(x+1)}{\log_7e}=\ln(3x^2+1)

x=? x=\text{?}

Video Solution

Answer

1,0 1,0

Exercise #18

12log3(x4)=log3(3x2+5x+1) \frac{1}{2}\log_3(x^4)=\log_3(3x^2+5x+1)

x=? x=\text{?}

Video Solution

Answer

54±174 -\frac{5}{4}\pm\frac{\sqrt{17}}{4}

Exercise #19

log4(3x2+8x10)log4(x2x+12.5)=0 \log_4(3x^2+8x-10)-\log_4(-x^2-x+12.5)=0

?=x

Video Solution

Answer

3.75,1.5 -3.75,1.5

Exercise #20

x=? x=\text{?}

ln(x+5)+lnxln4+ln2x \ln(x+5)+\ln x≤\ln4+\ln2x

Video Solution

Answer

0 < X \le 3