Question

determine x na PA ( x + 1, 2x, x2 - 5 )?

Answer 1

a1 = x + 1
a2 = 2x
a3 = x² - 5

a1 + a3 = 2 ( a2)
( x + 1 ) + ( x² - 5) = 2 ( 2x)
x² + x -4 = 4x
x² + x - 4 - 4x = 0
x² -3x - 4 = 0
delta = 9 + 16 = 25 = +-V25 = +-5 ***
x = ( 3 +-5)/2 
x1 = 8/2 = 4 ****
x2 = -2/2 = -1 ***