SOLUTION: D1: Let’s combine our knowledge of solving systems and solving logarithmic equations. Solve the system of equations: log yx = 3, this is log with a base of y, then x equals 3. l

Algebra ->  Exponential-and-logarithmic-functions -> SOLUTION: D1: Let’s combine our knowledge of solving systems and solving logarithmic equations. Solve the system of equations: log yx = 3, this is log with a base of y, then x equals 3. l      Log On


   



Question 948326: D1: Let’s combine our knowledge of solving systems and solving logarithmic equations. Solve the system of equations:
log yx = 3, this is log with a base of y, then x equals 3.
log y (4x) = 5, this is log with a base of y,(4x) equals 5.
I am trying to figure this question out. I need steps involved please.

Found 2 solutions by josgarithmetic, MathLover1:
Answer by josgarithmetic(39620) About Me  (Show Source):
You can put this solution on YOUR website!
Equations are
log(y,x)=3,log(y,(4x))=5
as rendered become the system
system%28log%28y%2Cx%29=3%2Clog%28y%2C%284x%29%29=5%29


The second equation is log%28y%2C4%29%2Blog%28y%2Cx%29=5.
Substitute using the first equation for log%28y%2Cx%29;

log%28y%2C4%29%2B3=5
log%28y%2C4%29=2
put into exponential form,
y%5E2=4
highlight%28y=-2%29 or highlight%28y=2%29.

Answer by MathLover1(20850) About Me  (Show Source):
You can put this solution on YOUR website!
log+%28y%2Cx%29+=+3...change the base to base 10
log+%28x%29%2Flog+%28y%29+=+3
log+%28x%29+=+3log+%28y%29
log+%28x%29+=+log+%28y%5E3%29...if log same, then we have
x+=+y%5E3 ...........eq.1
log+%28y%2C%284x%29%29+=+5
log+%28%284x%29%29%2Flog+%28y%29+=+5
log+%28%284x%29%29+=+5log+%28y%29
log+%28%284x%29%29+=+log+%28y%5E5%29=>
4x+=+y%5E5
x+=+y%5E5%2F4..............eq.2
system is:
x+=+y%5E3 ...........eq.1
x+=+y%5E5%2F4..............eq.2
since left sides same, right sides must be equal too
y%5E3=y%5E5%2F4...divide by y%5E3
4y%5E3%2Fy%5E3=y%5E5%2Fy%5E3
4=y%5E2
y=sqrt%284%29
solutions:
=>y=2 or y=-2

now find x
x+=+y%5E3 ...........if y=2
x+=+2%5E3
x+=+8
x+=+y%5E3 ...........if y=-2
x+=+%28-2%29%5E3
x+=+-8

intersection points:
(0,0)
(8,2)
(-8,-2)
check if all satisfy log
since we need log+%28y%2Cx%29+=+3=> log+%280%2C0%29+%3C%3E+3-this is not solution we can use

and log+%28y%2Cx%29+=+3=> highlight%28log+%282%2C8%29+=+3%29-this is solution we can use
and log+%28y%2Cx%29+=+3=> log+%282%2C-8%29+%3C%3E+3-this is not solution we can use either