We need to solve for x in the equation (31)16−2x2x2−2x=4x9.
2. Solution Steps
First, rewrite the equation. Since 31=3−1 and 9=3, we have:
(3−1)16−2x2x2−2x=4x⋅3
316−2x2−x2+2x=4x⋅31
316−2x2−x2+2x=(22)x⋅31
316−2x2−x2+2x=22x⋅31
Taking the logarithm base 3 on both sides is not helpful because of the term 22x.
Let's try rewriting the original equation as follows:
(31)16−2x2x2−2x=4x⋅9
(31)16−2x2x2−2x=4x⋅3
Rewrite the equation by taking logarithms with base 10 on both sides:
log((31)16−2x2x2−2x)=log(4x⋅3)
16−2x2x2−2xlog(31)=log(4x)+log(3)
16−2x2x2−2xlog(3−1)=xlog(4)+log(3)
16−2x2x2−2x(−log(3))=xlog(4)+log(3)
−16−2x2x2−2xlog(3)=xlog(4)+log(3)
Divide both sides by log(3):
−16−2x2x2−2x=xlog(3)log(4)+1
−16−2x2x2−2x=xlog3(4)+1
Another approach: let's try to get rid of 4x:
(31)16−2x2x2−2x=4x⋅3
If x=0, then (31)160=40⋅3, so 1=1⋅3, which means 1=3, which is false.
If x=−1, then (31)16−21+2=(31)143=4−1⋅3=43
(31)143≈0.7534, so 43=0.75. Therefore, x=−1 could be an approximate solution.
Let x=−2: (31)16−84+4=(31)88=31=4−2⋅3=161⋅3=163. This is also false.
Now let's simplify our original equation:
316−2x22x−x2=4x⋅31
316−2x22x−x2−1=4x
316−2x22x−x2−16+2x2=4x
316−2x2x2+2x−16=4x
If x=−4, 316−3216−8−16=3−16−8=321=3. Then 4−4=2561. So x=−4 is not a solution.
The equation can be rewritten as:
(31)16−2x2x2−2x=3⋅(22)x
(31)16−2x2x2−2x=3⋅22x
(31)16−2x2x2−2x=31⋅4x
316−2x22x−x2=31⋅4x
Take the natural logarithm of both sides:
ln(316−2x22x−x2)=ln(31⋅4x)
16−2x22x−x2ln(3)=ln(3)+xln(4)
ln(3)(16−2x22x−x2−1)=xln(4)
16−2x22x−x2−1=xln(3)ln(4)
16−2x22x−x2−(16−2x2)=xlog3(4)
16−2x22x−x2−16+2x2=xlog3(4)
16−2x2x2+2x−16=xlog3(4)
x2+2x−16=xlog3(4)(16−2x2)
x2+2x−16=16xlog3(4)−2x3log3(4)
2log3(4)x3+x2+(2−16log3(4))x−16=0
We can observe that if x=2, the left side of the original equation is (31)16−84−4=(31)0=1. The right side is 429=16⋅3=48.
Consider the case where the exponent 16−2x2x2−2x=0. This requires x2−2x=0, meaning x(x−2)=0, so x=0 or x=2. We have already shown x=0 is not a solution. If x=2, we have (31)0=429, or 1=16⋅3=48. Thus, x=2 is also not a solution.
Let's test x=−2. (31)16−84+4=(31)1=31. The right side is 4−29=161⋅3=163.
If x=21, then 16−2x2x2−2x=16−2141−1=231−43=−43⋅312=−623. Then the left side is (31)−623=3623≈1.0552. The right side is 41/2⋅3=2⋅3=6.
Consider x = -1: (31)16−21+2=(31)143≈(0.3333)0.214=0.7534. 4−19=41⋅3=43=0.75.