Question

Va rog sa imi explice cineva cum se fac .

Answer 1

4)   x, (2x+ 1), (4x + 5)
2x + 1= x·q  
4x + 5 = (2x+1)·q     (2x+1)/(4x+5) = x/(2x+1)     (2x+1)² = x(4x+5)
4x² + 4x + 1 = 4x² + 5x     x = 1      1, 3, 9....      3 = 1·3      9 = 1·3²
5) b3 - b1 = b1·q² - b1 = b1(q² - 1) = 16    b1(q+1)(q-1) =16
b4 - b2 = b1·q³ - b1·q² = q²·b1(q-1) = 48    (q+1)/q² = 1/3      q² = 3q + 3 
q² - 3q - 3 = 0     Δ = 9 + 12 = 21    q1 = (3 + √21)/2    q2 = (3 - √21)/2
6)  xn = 4n - 1   n < 14 ⇒ n ∈ {1,1,,,3,.....13} 
n = 1     x1 = 3    
 n2 = 2     x2 = 7 (7 = 3+1·4) 
n = 3     x3 = 11    (11= 3 + 2·4) 
n = 4     x4 = 15   (15 = 3 +3·4) 
4n - 1 = 4n + 3 - 4 = 3 + (n-1)·4     x1 = 3   r = 4