nilai n yang memenuhi persamaan 1/2n + 1/2n+2 = 9/40

1/2n + 1/2n+2 = 9/40
(2n+2 + 2n)/ 2n(2n+2)= 9/40
4n+2 / 4n² + 4n = 9/40
————————— kali silang
40(4n+2)= 9(4n²+4n)
160n + 80 = 36n² + 36n
36n²-160n +36n -80 =0
36n² - 124n -80 = 0
—————————— dibagi 4
9n² - 31n - 20 =0

-b +/- √b²-4ac / 2a
= 31 +/- √961 - 4(9)(-20) / 2(9)
= 31 +/- √961 + 720 /18
= 31 +/- √ 1681 /18
= 31 +/- 41 /18

n1 = 31+41 /18 = 72/18 = 4
»—————————————«
n2= 31-41 /18 = -10/18 = -5/9