Log3(x-2)+log3(x+6)=2

Лебедев Дмитрий Сергеевич

Учитель математики

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To solve the equation log3(x2)+log3(x+6)=2log base 3 of open paren x minus 2 close paren plus log base 3 of open paren x plus 6 close paren equals 2, follow these logical steps: 1. Determine the Domain (ODZ) The argument of a logarithm must be strictly greater than zero. Therefore, we must satisfy the following system of inequalities:

  • x2>0x>2x minus 2 is greater than 0 ⟹ x is greater than 2 x+6>0x>-6x plus 6 is greater than 0 ⟹ x is greater than negative 6

The intersection of these conditions is x>2x is greater than 2. Any potential solution must fall within this range. 2. Apply Logarithmic Properties Using the product rule for logarithms, logb(m)+logb(n)=logb(mn)log base b of m plus log base b of n equals log base b of open paren m center dot n close paren, we can combine the left side: log3((x2)(x+6))=2log base 3 of open paren open paren x minus 2 close paren open paren x plus 6 close paren close paren equals 23. Convert to Exponential Form By the definition of a logarithm ( logb(a)=cbc=alog base b of a equals c ⟺ b to the c-th power equals a), we rewrite the equation: (x2)(x+6)=32open paren x minus 2 close paren open paren x plus 6 close paren equals 3 squared (x2)(x+6)=9open paren x minus 2 close paren open paren x plus 6 close paren equals 94. Solve the Quadratic Equation Expand the brackets and move all terms to one side: x2+6x2x12=9x squared plus 6 x minus 2 x minus 12 equals 9 x2+4x129=0x squared plus 4 x minus 12 minus 9 equals 0 x2+4x21=0x squared plus 4 x minus 21 equals 0Using the quadratic formula or Vieta's formulas:

  • Sum of roots: x1+x2=-4x sub 1 plus x sub 2 equals negative 4 Product of roots: x1x2=-21x sub 1 center dot x sub 2 equals negative 21

The roots are:

  • x1=3x sub 1 equals 3
  • x2=-7x sub 2 equals negative 7

5. Verify Against the Domain We check each root against our initial condition ( x>2x is greater than 2):

  • x=3x equals 3: 3>23 is greater than 2 (Valid) x=-7x equals negative 7: -7<2negative 7 is less than 2 (Invalid/Extraneous)

Answer: x=3x equals 3 Would you like me to solve another logarithmic equation or demonstrate how to check the result by substituting it back into the original equation?

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