Ex 5.2, 7 - Chapter 5 Class 10 Arithmetic Progressions

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