Answer:
x = 25
Step-by-step explanation:
Log10 ( x - 21 ) + Log10 ( x ) = 2,
Log10 ( ( x - 21 )x ) = 2,
( x - 21 )x = 100,
Simplify:
x^2 - 21x = 100,
x^2 - 21x - 100 = 0,
x = - ( -21 ) + √ ( -21 )^2 - 4 * 1 ( -100 )/2 * 1 : 25
and
x = - ( -21 ) + √ ( -21 )^2 - 4 * 1 ( -100 )/2 * 1 : -4
( x = 25 ) ⇒ true
( x = - 4 ) ⇒ false
Answer: x = 25
