Maths about Log

Find the value without using the
calculator:

2log√2+log5

Sol

2log√2+log5

=log2+log5

=log10

=1



Solve the question:

[log(x+1)]^2－log(x+1)－12=0

Set y=log(x+1)

y^2－y－12=0

(y－4)(y+3)=0

y=4 oy y=-3

(1) y=4

log(x+1)=4

x+1=10^4=10000

x=9999

(2) log(x+1)=-3

x+1=10^(－3)=0.001

x=－0.999