Westonci.ca is your go-to source for answers, with a community ready to provide accurate and timely information. Connect with a community of experts ready to provide precise solutions to your questions quickly and accurately. Join our platform to connect with experts ready to provide precise answers to your questions in different areas.

Let [tex]\( T_r \)[/tex] be the [tex]\( r^{\text{th}} \)[/tex] term of an A.P. for [tex]\( r = 1, 2, \ldots \)[/tex].

Given that for some positive integers [tex]\( m \)[/tex] and [tex]\( n \)[/tex], we have [tex]\( T_m = \frac{1}{n} \)[/tex] and [tex]\( T_n = \frac{1}{m} \)[/tex],

Find [tex]\( T_{mn} \)[/tex].

Sagot :

To solve for [tex]\( T_{mn} \)[/tex], the [tex]\( mn \)[/tex]-th term of the given arithmetic progression (AP) where [tex]\( T_r \)[/tex] denotes the [tex]\( r \)[/tex]-th term, given that:

[tex]\[ T_m = \frac{1}{n} \][/tex]
[tex]\[ T_n = \frac{1}{m} \][/tex]

we start by understanding the general form of the [tex]\( r \)[/tex]-th term of an AP:

[tex]\[ T_r = a + (r - 1)d \][/tex]

where [tex]\( a \)[/tex] is the first term and [tex]\( d \)[/tex] is the common difference.

Given [tex]\( T_m \)[/tex] and [tex]\( T_n \)[/tex], we write the following two equations using the general formula:

[tex]\[ T_m = a + (m - 1)d = \frac{1}{n} \][/tex]
[tex]\[ T_n = a + (n - 1)d = \frac{1}{m} \][/tex]

To find [tex]\( a \)[/tex] and [tex]\( d \)[/tex], we solve these two linear equations simultaneously.

Substitute [tex]\( T_m = \frac{1}{n} \)[/tex] and [tex]\( T_n = \frac{1}{m} \)[/tex] into the equations:

[tex]\[ a + (m - 1)d = \frac{1}{n} \][/tex]
[tex]\[ a + (n - 1)d = \frac{1}{m} \][/tex]

By eliminating [tex]\( a \)[/tex] from these equations, we subtract the second equation from the first:

[tex]\[ (a + (m - 1)d) - (a + (n - 1)d) = \frac{1}{n} - \frac{1}{m} \][/tex]

[tex]\[ (m - 1)d - (n - 1)d = \frac{1}{n} - \frac{1}{m} \][/tex]

Simplify the left side:

[tex]\[ (m - 1 - (n - 1))d = \frac{1}{n} - \frac{1}{m} \][/tex]

[tex]\[ (m - n)d = \frac{1}{n} - \frac{1}{m} \][/tex]

Notice the right side can be simplified using a common denominator:

[tex]\[ (m - n)d = \frac{m - n}{mn} \][/tex]

Thus, the [tex]\( m - n \)[/tex] terms cancel out:

[tex]\[ d = \frac{1}{mn} \][/tex]

Now substitute [tex]\( d \)[/tex] back into one of the original equations to find [tex]\( a \)[/tex]. Using the first equation:

[tex]\[ a + (m - 1)\frac{1}{mn} = \frac{1}{n} \][/tex]

[tex]\[ a + \frac{m - 1}{mn} = \frac{1}{n} \][/tex]

Clearing the fractions by multiplying through by [tex]\( mn \)[/tex]:

[tex]\[ a \cdot mn + (m - 1) = m \][/tex]

[tex]\[ a \cdot mn = m - (m - 1) \][/tex]

[tex]\[ a \cdot mn = 1 \][/tex]

[tex]\[ a = \frac{1}{mn} \][/tex]

With [tex]\( a \)[/tex] and [tex]\( d \)[/tex] determined, we can find [tex]\( T_{mn} \)[/tex]:

[tex]\[ T_{mn} = a + (mn - 1)d \][/tex]

Substitute [tex]\( a = \frac{1}{mn} \)[/tex] and [tex]\( d = \frac{1}{mn} \)[/tex]:

[tex]\[ T_{mn} = \frac{1}{mn} + (mn - 1)\frac{1}{mn} \][/tex]

Distribute and simplify:

[tex]\[ T_{mn} = \frac{1}{mn} + \frac{mn - 1}{mn} \][/tex]

Combine the fractions:

[tex]\[ T_{mn} = \frac{1 + (mn - 1)}{mn} \][/tex]

[tex]\[ T_{mn} = \frac{mn}{mn} \][/tex]

[tex]\[ T_{mn} = 1 \][/tex]

Thus, the term [tex]\( T_{mn} \)[/tex] is:

[tex]\[ T_{mn} = \frac{(mn - 1) + 1}{mn} = \frac{mn}{mn} = 1 \][/tex]