If the third term of a GP is 4, then the product of first five terms of the GP is
[amp_mcq option1=”43” option2=”44” option3=”45” option4=”46” correct=”option3″]
Let the first term of the GP be ‘a’ and the common ratio be ‘r’.
The terms of the GP are:
1st term: $T_1 = a$
2nd term: $T_2 = ar$
3rd term: $T_3 = ar^2$
4th term: $T_4 = ar^3$
5th term: $T_5 = ar^4$
We are given that the third term of the GP is 4.
$T_3 = ar^2 = 4$.
We need to find the product of the first five terms of the GP.
Product P = $T_1 \times T_2 \times T_3 \times T_4 \times T_5$
P = $a \times (ar) \times (ar^2) \times (ar^3) \times (ar^4)$
Let’s group the ‘a’ terms and the ‘r’ terms:
P = $(a \times a \times a \times a \times a) \times (r^0 \times r^1 \times r^2 \times r^3 \times r^4)$
P = $a^5 \times r^{(0+1+2+3+4)}$
P = $a^5 \times r^{10}$
We can rewrite this expression by grouping $(ar^2)$ terms:
P = $a^5 \times r^{10} = (a^5 \times r^{10/5 \times 5}) = (a^5 \times r^{2 \times 5})$
P = $(a \times r^2)^5$
P = $(ar^2)^5$
We know that $ar^2 = 4$.
Substitute the value of $ar^2$ into the expression for P:
P = $(4)^5 = 4^5$.
– The product of the first n terms of a GP is $a^n r^{n(n-1)/2}$.
– The product of the first 5 terms is $a^5 r^{10}$.
– This can be rewritten as $(ar^2)^5$, which utilizes the given third term.