Question

4. Which term of the AP:3, 8, 13, 18, ...,is 78?
5. Find the number of terms in each of the following Ap

please answer mu question very fast​

Answer 1

AnsWer :

16.

SolutioN :

Let,

• First term be ' a '
• Common difference be ' d '

Now,

• a = 3.
• d = 5.

→ an = a + ( n -1 )d

Where as,

• a first term ( Let )
• d Common difference ( Let )

$\rule{90}2$

→ 78 = 3 + ( n - 1 )5

→ 78 - 3 = ( n - 1 )5

→ 75/ 5 = n - 1.

→ 15 = n - 1.

→ n = 16.

Therefore, the 16th terms of an AP is 78.

$\rule{200}3$

Some Information :

an = a + ( n - 1 )d.

Sn = n / 2 [ 2a + ( n - 1 )d]

Answer 2

$\large\sf{\underline{\red{\maltese\:{\underline{\blue{Question}}}}}}$

Which term of the AP:3, 8, 13, 18, ...,is 78 ? Find the number of terms in each of the following A.P.

$\large\sf{\underline{\red{\underline{\maltese\:{\green{Given}}}}}}$

• Common difference = (d)= 8-3 = 5
• 1st term (a)= 3
• last term $\sf a_n=78$

$\large\sf{\underline{\red{\maltese\:{\underline{\green{To\:Find}}}}}}$

• the number of terms in each of the following A.P (n)=?

$\sf{\underline{\red{\underline{\maltese\:{\green{FORMULA USED:-}}}}}}$

$\sf{\fbox{\blue{\underline{\red{a_n= a+(n-1)d}}}}}$

$\sf{\underline{\red{\maltese\:{\underline{\green{Substitute\: all\: values\:in\: Formula:-}}}}}}$

$\sf{\underline{\red{\underline{\green{\maltese\:{Solution}}}}}}$

$\sf→ a_n=a+(n-1)d\\\sf→ 78=3+(n-1)×5\\\sf→ 78-3=(n-1)5\\\sf→ 75=(n-1)5\\\sf→ \frac{75}{5}=(n-1)\\\ →15=n-1\\\sf→ n= 15+1\\\sf{\fbox{\red{\underline{\maltese\:{\blue{n=16}}}}}}$