double square root problem?
posted by Knights .
Hi I do not how to simplify the problem
x^2 =40+12sqrt2
what would be x? BTW if you sqrt both sides it would be double square root so what then? how to simplify?

12 sqrt 2 = x^2  40
144 (2) = x^4 80 x^2 + 1600
x^4  80 x^2 + 1312 = 0
graph to find zeros
http://mathportal.org/calculators/polynomialssolvers/polynomialgraphingcalculator.php
zeros at
x = 7.55, 4.80 + 4.80, +7.55
check those in original
+ and  7.55 works
the 4.8 does not