Ex 5.2, 2 - Chapter 5 Class 10 Arithmetic Progressions

Transcript

Ex 5.2 ,2 (i) Choose the correct choice in the following and justify 30th term of the A.P: 10, 7, 4, …, is A. 97 B. 77 C. − 77 D. − 87 10 , 7, 4, …. We know that an = a + (n – 1) d We have to find 30th term So, n = 30 Also, a = 10 & d = 7 – 10 = – 3 Putting these in formula a30 = 10 + (30 – 1) × ( – 3) = 10 + 29 × ( – 3) = 10 + (– 87) = – 77 So, option C is correct Ex 5.2 ,2 (ii) Choose the correct choice in the following and justify 11th term of the A.P. – 3, – 1/2, 2….. is A. 28 B. 22 C. − 38 D. –48 1/2 – 3, (− 1)/2 , 2, … We know that an = a + (n – 1) d We have to find 11th term i.e. n = 11 Also, a = – 3 d = (−1)/2 – ( – 3) = (− 1)/2 + 3 = (− 1 + 6)/2 = 5/2 Putting these in formula a11 = – 3 + (11 – 1) × 5/2 = – 3 + 10 × ( 5)/2 = – 3 + 5 × 5 = – 3 + 25 = – 22 So, the answer is (B)