If ×=log3 and y=log21, write an expression for log square root 7 in terms of x and y

Answer is      (1/2)y - (1/2)x======x = log 3 and y = log 21note that 21 factors into 3 and 7 so    y = log 21    y = log(7  · 3)use log law that says      y = log(7) + log(3)and since x = log(3):     y = log(7) + xsolve for log(7) to get    log 7 = y - xnow focusing on    use log law  with      since log 7 = y - x