20=-10n+3n+7n∧²/2这个怎么算,

20=-10n+3n+7n∧²/2这个怎么算,
20=-10n+3n+7n∧²/2这个怎么算,

20=-10n+3n+7n∧²/2这个怎么算,
20=-10n+3n+7n∧²/2
20=-7n+7n∧²/2
40=-14n+7n∧²
7n∧²-14n=40
n∧²-2n=40/7
n∧²-2n+1=40/7+7/7
(n-1)^2=47/7
n-1=±√329/7
n=1±√329/7