Friday, February 27, 2015

Solve the equation (3+2sqrt2)^x + (3-2sqrt2)^x=34

The given equation is an exponential equation and we'll
solve it using the substitution technique.


We notice that
(3+2sqrt2)*(3-2sqrt2) = 3^2 -
(2sqr2)^2


(3+2sqrt2)*(3-2sqrt2) = 9 -
4*2


(3+2sqrt2)*(3-2sqrt2) = 9 -
8


(3+2sqrt2)*(3-2sqrt2) =
1


We'll raise to x power both
sides:


[(3+2sqrt2)*(3-2sqrt2)]^x =
1^x


(3+2sqrt2)^x*(3-2sqrt2)^x =
1


(3+2sqrt2)^x = 1 /
(3-2sqrt2)^x


We'll note (3+2sqrt2)^x =
t


t = 1 /
(3-2sqrt2)^x


(3-2sqrt2)^x =
1/t


We'll substitute in the given
equation:


t + 1/t = 34


t^2 + 1
- 34t = 0


t^2  - 34t + 1 =
0


We'll apply the quadratic
formula:


t1 =
(34+sqrt1152)/2


t1 =
(34+24sqrt2)/2


t1 = 17 +
12sqrt2


t2 = 17 -
12sqrt2


(3+2sqrt2)^x = 17 +
12sqrt2


lg (3+2sqrt2)^x = lg (17 +
12sqrt2)


x*lg (3+2sqrt2) = lg (17 +
12sqrt2)


x1 = lg (17 + 12sqrt2) / lg
(3+2sqrt2)


x2 = lg (17 - 12sqrt2) / lg
(3+2sqrt2)

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