Question

determine valor de x em (x-1,2x,5x+6) em p.a

Answer 1

$2a_n=a_{n-1}+a_{n+1},\ para\ n\ge2,\ n\in\mathbb{R}\\\\2a_2=a_{2-1}+a_{2+1}\\\\2a_2=a_{1}+a_{3}\\\\2(2x)=(x-1)+(5x+6)\\\\4x=x-1+5x+6\\\\4x=6x+5\\\\6x-4x=-5\\\\2x=-5\\\\\boxed{x=-\dfrac{5}{2}}$