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| 1. |
The sum of 4 th and 8th term is 24 and the sum of 6th and 10 th term is 44 .Find AP |
| Answer» Let the first term and the common difference of the AP be a and d respectively.Then,4th term = a + (4 - 1)d = a + 3d\xa0{tex}\\because {a_n} = a + (n - 1)d{/tex}8th term = a + (8 - 1)d = a + 7d\xa0{tex}\\because {a_n} = a + (n - 1)d{/tex}6th term = a + (6 - 1)d = a + 5d\xa0{tex}\\because {a_n} = a + (n - 1)d{/tex}and 10th term = a + (10 - 1)d = a + 9d\xa0{tex}\\because {a_n} = a + (n - 1)d{/tex}According to the question,4th term + 8th term = 24{tex} \\Rightarrow {/tex}\xa0(a + 3d) + (a + 7d) = 24{tex} \\Rightarrow {/tex}\xa02a + 10d = 24{tex} \\Rightarrow {/tex}\xa0a + 5d = 12 .......... (1) (Dividing throughout by 2)6th term + 10th term = 24{tex} \\Rightarrow {/tex}\xa0(a + 5d) + (a + 9d) = 44{tex} \\Rightarrow {/tex}\xa02a + 14d = 44{tex} \\Rightarrow {/tex}\xa0a + 7d = 22 .......... (2) (Dividing throughout by 2)Solving (1) and (2), we geta = -13d = 15So, First term = -13Second term = -13 + 5 = -8Third term = -8 + 5 = -3Hence, the first three terms of the given AP are -13, -8 and -3. | |