Find the sum (up to 3 decimal places) of all the irrational values of satisfying the above equation.
This section requires Javascript.
You are seeing this because something didn't load right. We suggest you, (a) try
refreshing the page, (b) enabling javascript if it is disabled on your browser and,
finally, (c)
loading the
non-javascript version of this page
. We're sorry about the hassle.
Our four cases and their discriminants (from previous problem(s)):
Case 1: 3 x 2 + 3 = 1 0 x
Since both sides have the same base, if the powers are equal, the two sides will equal each other.
Discriminant: 6 4
Case 2: x 2 + x − 5 7 = 0
Zero to any positive power will equal zero, so both sides will equal regardless of having different powers.
Discriminant: 2 2 9
Case 3: x 2 + x − 5 7 = 1
Similarly, 1 to any power will equal 1.
Discriminant: 2 3 3
Case 4: x 2 + x − 5 7 = − 1
As long as the powers on both sides are either both even or both odd, -1 to a power will equal 1 and -1, respectively.
Discriminant: 2 2 5
We see that the second and third equations have positive but non perfect square roots, so they will yield irrational solutions.
Using the quadratic formula on the second equation, 2 − b ± b 2 − 4 a c , gives us the solutions x = 2 − 1 ± 2 2 9 .
These solutions will make the base 0 , but we must check to see what they make the powers, 3 x 2 + 3 a n d 1 0 x , because if the power(s) is negative, then it would equal 0 n 1 , which is undefined.
Substituting in x = 2 − 1 + 2 2 9 ,
3 ( 2 − 1 + 2 2 9 ) 2 + 3 ≅ 2 4 . 1 9 9
1 0 ( 2 − 1 + 2 2 9 ) ≅ 7 0 . 6 6 4
Therefore, this solution works.
Substituting in x = 2 − 1 − 2 2 9 ,
3 ( 2 − 1 − 2 2 9 ) 2 + 3 ≅ 1 9 8 . 1 9 9
1 0 ( 2 − 1 + 2 2 9 ) ≅ − 8 0 . 6 6 4
The 1 0 x power becomes negative, and therefore, this is not a valid solution.
Using the quadratic equation on the third equation, we get x = 2 − 1 ± 2 3 3
Since 1 raised to any power, positive or negative, is 1, these solutions work.
Adding up the solutions, we get 2 − 1 + 2 3 3 + 2 − 1 − 2 3 3 + 2 − 1 + 2 2 9 ≅ 6 . 0 6 6