Oxford University Entrance Exam Tricks | 1 % Passed Admission Aptitude Test

[@9허공]

4x^2 - 4y^2 = 1 => 4(x + y)(x - y) = 1 => 16(x + y)^2*(x - y)^2 = 1 ---(1)
let a = x + y => (x + y)^2 = (x - y)^2 + 4xy => (x - y)^2 = (x + y)^2 - 4xy = a^2 - 1
from eq. (1) 16 * a^2 * (a^2 - 1) = 1 => 16a^4 - 16a^2 - 1 = 0
=> a^2 = (2 +√5)/4 => a = x + y = ± √(2 + √5)/2

[@RealQinnMalloryu4]

(4x^2)^2 ➖(4y^2)^2={16x^4 ➖ 16y^4}={0+0 ➖ xy^0+0 ➖ }=1xy^1(xy ➖ 1xy+1) . 2^2xy (xy ➖ 2xy+2).