Question

Determine a pg (k-1,2k,4k+5)

Answer 1

u1 = k - 1 
u2 = 2k 
u3 = 4k + 5

u2² = u1*u3 

4k² = (k - 1)*(4k + 5)
4k² = 4k² + k - 5 

k - 5 = 0
k = 5

PG

u1 = k - 1 = 5 - 1 = 4
u2 = 2k = 2*5 = 10
u3 = 4k + 5 = 4*5 + 5 = 25