((n+1)!)/((n-1)!)=20

解答

\frac{( n + 1 ) !}{( n - 1 ) !} = 20

n = 4, n = - 5

求解步骤

\frac{( n + 1 ) !}{( n - 1 ) !} = 20

化简

\frac{( n + 1 ) !}{( n - 1 ) !} : n (n + 1)

n (n + 1) = 20

解

n (n + 1) = 20 : n = 4, n = - 5

n = 4, n = - 5

so l v e f or t, s = \frac{d}{( t - t _{0} )}

\frac{3}{( x + \frac{1}{2} ) - x ^{2} + 3 x} = \frac{6}{( 2 x + 1 )} + x^{2} - 2

so l v e f or x, f (x - 3) = \frac{( x ^{2} - 9 )}{( x + 1 )}

80 x^{- 2} = 6 x^{- 1} + 2

(\frac{1 - 1}{x})^{10} = 0.8