The first four terms in a sequence of numbers are given below.

  1. (a)

    Find T5T_5.

    Answer ...

  2. (b)

    Find an expression, in terms of n, for TnT_n.

    Answer Tn=T_n=...

  3. (c)

    Evaluate the sum of the first ten terms, T1+T2+T3+⋯+T10T_1+T_2+T_3+\dots+T_{10}.

    Answer ...

Work through it with AI →

It won't just hand you the answer — it asks where you're stuck.How the checker works

Worked solution

20(a)

1. Continue the given pattern to form and evaluate $T_5$.

From the pattern,
T5=654−755T_5=\dfrac{6}{5^4}-\dfrac{7}{5^5}
=3055−755=\dfrac{30}{5^5}-\dfrac{7}{5^5}
=2355=233125=\dfrac{23}{5^5}=\dfrac{23}{3125}

Answer

T5=233125T_5=\dfrac{23}{3125}

20(b)

1. Identify the general form of the two fractions in $T_n$.

From the pattern,
T1=21−35,T2=35−452,T3=452−553.T_1=\frac{2}{1}-\frac{3}{5},\quad T_2=\frac{3}{5}-\frac{4}{5^2},\quad T_3=\frac{4}{5^2}-\frac{5}{5^3}.
So,
Tn=n+15n−1−n+25n.T_n=\frac{n+1}{5^{n-1}}-\frac{n+2}{5^n}.

2. Simplify the expression into a single fraction.

Tn=n+15n−1−n+25nT_n=\frac{n+1}{5^{n-1}}-\frac{n+2}{5^n}
=5(n+1)5n−n+25n=\frac{5(n+1)}{5^n}-\frac{n+2}{5^n}
=5n+5−n−25n=\frac{5n+5-n-2}{5^n}
=4n+35n.=\frac{4n+3}{5^n}.

Answer

Tn=4n+35nT_n=\dfrac{4n+3}{5^n}

20(c)

1. Write the first ten terms using the subtraction pattern.

From the given pattern,
Tn=n+15n−1−n+25n.T_n=\frac{n+1}{5^{n-1}}-\frac{n+2}{5^n}.
So

T1+T2+⋯+T10=(2−35)+(35−452)+(452−553)+⋯+(1159−12510).\begin{aligned} T_1+T_2+\cdots+T_{10} &=\left(2-\frac35\right)+\left(\frac35-\frac4{5^2}\right)+\left(\frac4{5^2}-\frac5{5^3}\right)+\cdots+\left(\frac{11}{5^9}-\frac{12}{5^{10}}\right). \end{aligned}

2. Cancel matching terms and evaluate the remaining expression.

All the middle terms cancel:
T1+T2+⋯+T10=2−12510.T_1+T_2+\cdots+T_{10}=2-\frac{12}{5^{10}}.

Answer

2−125102-\dfrac{12}{5^{10}}

AI analysis — may contain mistakes.

Worked this one out on paper? Snap your steps and Gigle's AI math checker will circle the step where it went wrong.

More questions on this topic

  1. 1Find the 8th term of the sequence 10, 11, 13, 16, 20,..., Answer
  2. 2The first four terms in a sequence of numbers are 3+k, 1+k, −1+k, −3+k, …3 + k,\ 1 + k,\ -1 + k,\ -3 + k,\ \dots where kk is a constant. Fin…
  3. 3Diagram 1 shows an equilateral triangle with sides of length 1 unit. An inverted white equilateral triangle with sides o…
  4. 4Study the pattern below. Write down the values of aa, bb and cc in Figure 11. Answer aa = ... bb = ... cc = ... Wr…
  5. 5Here are the first four terms of a sequence. 1351010715420\displaystyle \frac{13}{5}\quad \frac{10}{10}\quad \frac{7}{15}\quad \frac{4}{20}…