7 Solve each of the following equations.
a log3x+log35=log3(2x+3)
b log9x+log910=23
c log4x−log4(x−1)=log43+21
d log55x−log5(x+2)=log5(x+6)−log5x
e 2log6x=log6(2x−5)+log65
f log74x=log7x−61+1
8 Solve each pair of simultaneous equations.
a logxy=2xy=27
b log5x−2log5y=log52x+y2=12
c log2x=3−2log2y
d logyx=23logy32=−25x31+3y21=20
e logax+loga3=21logay
f log10y+2log10x=33x+y=20log2y−log2x=3
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Answer from Sia
Posted 6 months ago
Solution by Steps
step 1
Simplify the given equation using the properties of logarithms: log3x+log35=log3(2x+3)
step 2
Combine the logarithms on the left side: log3(5x)=log3(2x+3)
step 3
Since the bases and the arguments are equal, set the arguments equal to each other: 5x=2x+3
step 4
Solve for x by isolating it on one side: 5x−2x=3⟹3x=3⟹x=1
Question 7b
step 1
Simplify the given equation using the properties of logarithms: log9x+log910=23
step 2
Combine the logarithms on the left side: log9(10x)=23
step 3
Rewrite the equation in exponential form: 10x=93/2
step 4
Simplify the right side: 93/2=(32)3/2=33=27
step 5
Solve for x by isolating it on one side: 10x=27⟹x=1027=2.7
Question 7c
step 1
Simplify the given equation using the properties of logarithms: log4x−log4(x−1)=log43+21
step 2
Combine the logarithms on the left side: log4(x−1x)=log4(3⋅4)
step 3
Simplify the right side: log4(3⋅2)=log46
step 4
Since the bases and the arguments are equal, set the arguments equal to each other: x−1x=6
step 5
Solve for x by isolating it on one side: x=6(x−1)⟹x=6x−6⟹5x=6⟹x=56=1.2
Question 7d
step 1
Simplify the given equation using the properties of logarithms: log55x−log5(x+2)=log5(x+6)−log5x
step 2
Combine the logarithms on both sides: log5(x+25x)=log5(xx+6)
step 3
Since the bases and the arguments are equal, set the arguments equal to each other: x+25x=xx+6
step 4
Cross-multiply to solve for x: 5x2=(x+2)(x+6)⟹5x2=x2+8x+12
step 5
Simplify and solve the quadratic equation: 4x2−8x−12=0⟹x2−2x−3=0⟹(x−3)(x+1)=0
step 6
Solve for x: x=3 or x=−1 (since x must be positive, x=3)
Question 7e
step 1
Simplify the given equation using the properties of logarithms: 2log6x=log6(2x−5)+log65
step 2
Combine the logarithms on the right side: 2log6x=log6(5(2x−5))
step 3
Simplify the right side: 2log6x=log6(10x−25)
step 4
Rewrite the left side: log6(x2)=log6(10x−25)
step 5
Since the bases and the arguments are equal, set the arguments equal to each other: x2=10x−25
step 6
Solve the quadratic equation: x2−10x+25=0⟹(x−5)2=0⟹x=5
Question 7f
step 1
Simplify the given equation using the properties of logarithms: log74x=log7(x−61)+1
step 2
Rewrite the right side: log74x=log7(x−61)+log77
step 3
Combine the logarithms on the right side: log74x=log7(x−67)
step 4
Since the bases and the arguments are equal, set the arguments equal to each other: 4x=x−67
step 5
Cross-multiply to solve for x: 4x(x−6)=7⟹4x2−24x−7=0
step 6
Solve the quadratic equation using the quadratic formula: x=2⋅424±242+4⋅4⋅7=824±784=824±28
step 7
Simplify the solutions: x=852=6.5 or x=8−4=−0.5 (since x must be positive, x=6.5)
Answer
7a: x=1
7b: x=2.7
7c: x=1.2
7d: x=3
7e: x=5
7f: x=6.5
Key Concept
Logarithmic Equations
Explanation
To solve logarithmic equations, use properties of logarithms to combine or simplify terms, then convert to exponential form if necessary and solve for the variable.
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