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Solve: 0.05x^2.32> 4* 1.05^x-1?
4* 1.05^(x-1)
2 réponses
- AlanLv 7il y a 4 ans
if you meant
0.05*x^(2.32) > 4* 1.05^(x-1)
=== I believe the answer is
x> 7.59508046
=== why
multiple both sides by 20
x^2.32 > 80* 1.05^(x-1)
x^2.32 - 80* 1.05^(x-1)> 0
so find the equal "= " case first,
Then, you can try point above and below this point to determine the correct zone.
y = x^2.32 - 80* 1.05^(x-1)
so you are looking where y > 0 to meet the inequality.
Using Newton Raphson Method
graph the equation to show an area to guess
(or just try points looking for 0 crossings )
for example find f(7.4) and f(7.6)
f(7.4) = -5.419984155
f(7.6) = 0.139427036 , so 7.6 is greater than zero so it will be x> 7.XXXX
so you know one answer for equal point is between 7.4 < x< 7.6
Excel indicates for all negative values of x, the y are undefined.
for real numbers
and the only real answer about 7.5
x> 7.5XXXX
now just use newton raphson method to refine the answer
next guess = prev guess - f(x)/f'(x)
ng = pg - (x^2.32 - 80* 1.05^(x-1))/(2.32*(x^1.32) - 80*ln(1.05)*(1.05)^(x-1) )
pg adjustment New Guess
7.5 -0.095988095 7.595988095
7.595988095 0.000907554 7.595080541
7.595080541 8.13622E-08 7.59508046
7.59508046 4.01327E-15 7.59508046
7.59508046 -6.01991E-15 7.59508046
so according to Excel
x> 7.59508046
Desmos graphing utilities also shows negative value of x, but
everything I read tells me the graph is wrong.
Every time I tried to use Newton Raphson method with this
It says (-5.738)^(2.32) is undefined in real numbers
.I know you cannnot have negative even roots. (-5)^(-1/2) is undefined.
(-5)^(2.32) = (-5)^2*(-5)^(0.32)