Question

if a3 = 300 , a7= 800 find a20 ​

Answer 1

Given:

We have $a_3=300,a_7=800$

To Find:

We have to find $a_2_0?$

Step-by-step explanation:

• In an AP nth term is given by the formula

                     $a_n=a+(n-1)d$

• We have 3rd term of AP and 7th term of AP

               $a_3=300 \\and\\a_7=800$

• On comparing them with nth term equation we get

             $a+2d=300\\and\\a+6d=800$

• Now solve the both equation by substitution method we get

        $a=300-2d \\\textrm{put the value of a in other equation}\\300-2d+6d=800\\\\4d=500\\d=125\\\textrm{now put the value of d in other equation we get }\\a=50$

Thus 20th term will be

          $a_2_0=a+19d=50+19(125)\\\\a_2_0=2452$

Thus 20th term is 2452.