diketahui suatu barisan aritmatika u3=9 dan u7=37,maka suku ke-30 adalah...

U₇ = 37 = a + 6b
U₃ =   9 = a + 2b
      ------------------ -
        28 =       4b
          b = 7

U₃ = 9 = a + 2b
        9 = a + 2 (7)
        9 = a + 14
        a = -5

U₃₀ = a + 29b
      = -5 + 29 (7)
      = -5 + 203
      = 198

semoga jelas dan membantu ya

a+2b=9
a+6b=37

a= 9-2b
(9-2b)+6b= 37
4b = 37-9
b=28:4
b=7

a=9-(2×7)
a=9-14
a=-5

U30=a+(30-1)b
U30=-5+29×7
U30=-5+203 = 198