An algebra problem by prasanth pp

Algebra Level 2

If m = log 7 2 m = \log_7 2 , find the value of log 49 28 \log_{49} 28 in terms of m m .

1 + m 1+m 1 + 2 m 2 \frac{1+2m}{2} 2 1 + 2 m \frac{2}{1+2m} 2 ( 1 + 2 m ) 2(1+2m) 1 1 + 2 m \frac{1}{1+2m}

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1 solution

Prasanth Pp
Apr 10, 2016

Given l o g 7 2 = m . . . . . . . . . . . . . . . . . . . . ( 1 ) log_{7}2=m....................(1)

l o g 49 28 = l o g 7 28 l o g 7 49 log_{49}28= \frac{log_{7}28}{log_{7}49} (Note:base changing rule)

= l o g 7 ( 2 2 × 7 ) l o g 7 7 2 = \frac{log_{7}(2^{2} \times 7 )}{log_{7}7^{2}}
= ( l o g 7 7 ) + ( l o g 7 ( 2 2 ) 2 = \frac{(log_{7}7)+(log_{7}(2^{2} )}{2}
= 1 + 2 ( l o g 7 2 ) 2 = \frac{1+2(log_{7}2) }{2}
= 1 + 2 m 2 = \frac{1+2m}{2} (from...(1))

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