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Ex 5.2, 7 - Find 31st term of an A.P. whose 11th term - Finding nth term


Transcript

Ex 5.2 ,7 Find the 31st term of an A.P. whose 11th term is 38 and the 16th term is 73 We know that an = a + (n – 1) d From (1) & (2) 38 – 10d = 73 – 15d 38 – 73 = – 15d – 10d – 35 = –5d (−35)/(−5) = d 7 = d d = 7 Putting the value of d in (1) a = 38 – 10 d a = 38 – 10× 7 a = 38 – 70 a = – 32 We need to find the 31st term So, n = 31, a = – 32, d = 7 We need to find an an = a + (n – 1) d Putting values a31 = – 32 + (31 – 1) 7 = – 32 + 30 × 7 = – 32 + 210 = 178 Therefore, the 31st term of AP is 178

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