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b) The 3rd, 5th and 8th terms of another AP form the first three consecutive terms. If the common difference of AP is 3, find: i) The 1st term or GP.

Mathematics

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b) i)
Tunapewa kwamba neno la 3, la 5, na la 8 la AP nyingine huunda maneno matatu ya kwanza mfululizo ya GP.
Tofauti ya kawaida ya AP hii ni D=3D = 3.
Acha neno la kwanza la AP liwe AA.
Maneno ya AP ni:
Neno la 3: A3=A+(3−1)D=A+2D=A+2(3)=A+6A_3 = A + (3-1)D = A + 2D = A + 2(3) = A + 6
Neno la 5: A5=A+(5−1)D=A+4D=A+4(3)=A+12A_5 = A + (5-1)D = A + 4D = A + 4(3) = A + 12
Neno la 8: A8=A+(8−1)D=A+7D=A+7(3)=A+21A_8 = A + (8-1)D = A + 7D = A + 7(3) = A + 21

Maneno haya huunda GP, kwa hivyo:
G1=A+6G_1 = A + 6
G2=A+12G_2 = A + 12
G3=A+21G_3 = A + 21

  1. Tumia sifa ya GP kwamba uwiano wa kawaida (rr) kati ya maneno mfululizo ni sawa.

    r=G2G1=G3G2r = \frac{G_2}{G_1} = \frac{G_3}{G_2}

    Badilisha maneno ya GP:

    A+12A+6=A+21A+12\frac{A + 12}{A + 6} = \frac{A + 21}{A + 12}
  2. Tatua mlinganyo kwa AA.

    Panua pande zote mbili:

    (A+12)2=(A+6)(A+21)(A + 12)^2 = (A + 6)(A + 21) A2+24A+144=A2+21A+6A+126A^2 + 24A + 144 = A^2 + 21A + 6A + 126 A2+24A+144=A2+27A+126A^2 + 24A + 144 = A^2 + 27A + 126

    Toa A2A^2 kutoka pande zote mbili na panga upya:

    144−126=27A−24A144 - 126 = 27A - 24A 18=3A18 = 3A A=183A = \frac{18}{3} A=6A = 6
  3. Pata neno la kwanza la GP (G1G_1).

    Neno la kwanza la GP ni G1=A3=A+6G_1 = A_3 = A + 6.

    G1=6+6G_1 = 6 + 6 G1=12G_1 = 12

    Neno la kwanza la GP ni 12\boxed{12}.

    b) ii)
    Tunahitaji kupata jumla ya maneno 9 ya kwanza ya GP (S9S_9).
    Kutoka sehemu (i), tunajua neno la kwanza la GP ni G1=12G_1 = 12.

  4. Pata uwiano wa kawaida (rr) wa GP.

    r=G2G1=A+12A+6r = \frac{G_2}{G_1} = \frac{A + 12}{A + 6}

    Badilisha A=6A = 6:

    r=6+126+6=1812r = \frac{6 + 12}{6 + 6} = \frac{18}{12} r=32r = \frac{3}{2}
  5. Tumia fomula ya jumla ya maneno nn ya GP, Sn=G1(rn−1)r−1S_n = \frac{G_1(r^n - 1)}{r - 1} (kwa r>1r > 1).

    Badilisha maadili: G1=12G_1 = 12, r=32r = \frac{3}{2}, na n=9n = 9.

    S9=12((32)9−1)32−1S_9 = \frac{12\left(\left(\frac{3}{2}\right)^9 - 1\right)}{\frac{3}{2} - 1}
  6. Rahisisha mlinganyo.

    S9=12(3929−1)12S_9 = \frac{12\left(\frac{3^9}{2^9} - 1\right)}{\frac{1}{2}} S9=24(19683512−1)S_9 = 24\left(\frac{19683}{512} - 1\right) S9=24(19683−512512)S_9 = 24\left(\frac{19683 - 512}{512}\right) S9=24(19171512)S_9 = 24\left(\frac{19171}{512}\right)
  7. Fanya hesabu na toa jibu kwa idadi muhimu ya tarakimu (significant figures).

    S9=24×19171512S_9 = \frac{24 \times 19171}{512} S9=3×1917164S_9 = \frac{3 \times 19171}{64} S9=5751364S_9 = \frac{57513}{64} S9≈898.640625S_9 \approx 898.640625

    Kuzungusha kwa tarakimu 3 muhimu (3 significant figures):

    S9≈899S_9 \approx 899

    Jumla ya maneno 9 ya kwanza ya GP ni 899\boxed{899}.

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