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Question

Find x, if:

(i) log3x=0

(ii) logx2=1

(iii) log9243=x

(iv) log5(x7)=1

(v) log432=x7

(vi) log7(2x21)=2

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Solution

(i)

c o n s i d e r space space t h e space e q u a t i o n log subscript 3 x equals 0 rightwards double arrow 3 to the power of 0 equals x rightwards double arrow 1 equals x space

(ii)

c o n s i d e r space t h e space e q u a t i o n log subscript x 2 equals negative 1 rightwards double arrow x to the power of negative 1 end exponent equals 2 rightwards double arrow x equals 1 half

(iii)

c o n s i d e r space t h e space e q u a t i o n log subscript 9 243 equals x rightwards double arrow 9 to the power of x equals 243 rightwards double arrow open parentheses 3 squared close parentheses to the power of x equals 3 to the power of 5 rightwards double arrow 2 x equals 5 rightwards double arrow x equals 5 over 2

(iv)

c o n s i d e r space t h e space e q u a t i o n log subscript 5 open parentheses x minus 7 close parentheses equals 1 5 to the power of 1 equals x minus 7 x equals 7 plus 5 equals 12

(v)

c o n s i d e r space t h e space e q u a t i o n log subscript 4 32 equals x minus 4 rightwards double arrow 4 to the power of x minus 4 end exponent equals 32 rightwards double arrow open parentheses 2 squared close parentheses to the power of x minus 4 end exponent equals 2 to the power of 5 rightwards double arrow 2 open parentheses x minus 4 close parentheses equals 5 rightwards double arrow 2 x minus 8 equals 5 rightwards double arrow 2 x equals 13 rightwards double arrow x equals 13 over 2

(vi)log7(2x21)=2
72 = 2x21
49 + 1 = 2x2
25 = x2
x =+ 5 or -5


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