First, rewrite the square root as a power of 1/2:
log 10 10 a b 5 c = log 10 ( 10 a b 5 c ) 1 / 2 \log_{10} \sqrt{\frac{10a}{b^5 c}} = \log_{10} \left(\frac{10a}{b^5 c}\right)^{1/2} log 10 b 5 c 10 a = log 10 ( b 5 c 10 a ) 1/2
Use the power rule of logarithms: log b ( x p ) = p log b x \log_b (x^p) = p \log_b x log b ( x p ) = p log b x log 10 ( 10 a b 5 c ) 1 / 2 = 1 2 log 10 ( 10 a b 5 c ) \log_{10} \left(\frac{10a}{b^5 c}\right)^{1/2} = \frac{1}{2} \log_{10} \left(\frac{10a}{b^5 c}\right) log 10 ( b 5 c 10 a ) 1/2 = 2 1 log 10 ( b 5 c 10 a )
Use the quotient rule of logarithms: log b x y = log b x − log b y \log_b \frac{x}{y} = \log_b x - \log_b y log b y x = log b x − log b y 1 2 log 10 ( 10 a b 5 c ) = 1 2 [ log 10 ( 10 a ) − log 10 ( b 5 c ) ] \frac{1}{2} \log_{10} \left(\frac{10a}{b^5 c}\right) = \frac{1}{2} \left[\log_{10}(10a) - \log_{10}(b^5 c)\right] 2 1 log 10 ( b 5 c 10 a ) = 2 1 [ log 10 ( 10 a ) − log 10 ( b 5 c ) ]
Use the product rule of logarithms: log b ( x y ) = log b x + log b y \log_b (xy) = \log_b x + \log_b y log b ( x y ) = log b x + log b y 1 2 [ log 10 ( 10 a ) − log 10 ( b 5 c ) ] = 1 2 [ log 10 10 + log 10 a − ( log 10 b 5 + log 10 c ) ] \frac{1}{2} \left[\log_{10}(10a) - \log_{10}(b^5 c)\right] = \frac{1}{2} \left[\log_{10} 10 + \log_{10} a - (\log_{10} b^5 + \log_{10} c)\right] 2 1 [ log 10 ( 10 a ) − log 10 ( b 5 c ) ] = 2 1 [ log 10 10 + log 10 a − ( log 10 b 5 + log 10 c ) ]
Use the power rule of logarithms again:
1 2 [ log 10 10 + log 10 a − ( log 10 b 5 + log 10 c ) ] = 1 2 [ log 10 10 + log 10 a − ( 5 log 10 b + log 10 c ) ] \frac{1}{2} \left[\log_{10} 10 + \log_{10} a - (\log_{10} b^5 + \log_{10} c)\right] = \frac{1}{2} \left[\log_{10} 10 + \log_{10} a - (5\log_{10} b + \log_{10} c)\right] 2 1 [ log 10 10 + log 10 a − ( log 10 b 5 + log 10 c ) ] = 2 1 [ log 10 10 + log 10 a − ( 5 log 10 b + log 10 c ) ]
Since log 10 10 = 1 \log_{10} 10 = 1 log 10 10 = 1 , we have: 1 2 [ 1 + log 10 a − ( 5 log 10 b + log 10 c ) ] \frac{1}{2} \left[1 + \log_{10} a - (5\log_{10} b + \log_{10} c)\right] 2 1 [ 1 + log 10 a − ( 5 log 10 b + log 10 c ) ]
Now substitute the given values log 10 a = x \log_{10} a = x log 10 a = x , log 10 b = y \log_{10} b = y log 10 b = y , and log 10 c = z \log_{10} c = z log 10 c = z : 1 2 [ 1 + x − ( 5 y + z ) ] = 1 2 [ 1 + x − 5 y − z ] \frac{1}{2} \left[1 + x - (5y + z)\right] = \frac{1}{2} \left[1 + x - 5y - z\right] 2 1 [ 1 + x − ( 5 y + z ) ] = 2 1 [ 1 + x − 5 y − z ]