How do you solve #logx+log(x+21)=2#? Precalculus Properties of Logarithmic Functions Common Logs 1 Answer erinspoons Nov 23, 2016 #x=25# Explanation: #logx(x+21)=2# #log(x^2+21x)=2# #x^2+21x=10^2# #x^2+21x-100=0# #(x-4)(x+25)=0# #x=4# and #x=-25# #x=-25# is extraneous #x=4# Answer link Related questions What is the common logarithm of 10? How do I find the common logarithm of a number? What is a common logarithm or common log? What are common mistakes students make with common log? How do I find the common logarithm of 589,000? How do I find the number whose common logarithm is 2.6025? What is the common logarithm of 54.29? What is the value of the common logarithm log 10,000? What is #log_10 10#? How do I work in #log_10# in Excel? See all questions in Common Logs Impact of this question 5567 views around the world You can reuse this answer Creative Commons License