The 21st term of an A.P., whose first two terms are -3 and 4 is ……

1.	The 21st term of an A.P., whose first two terms are -3 and 4 is ………………A) 143 B) -143C) 137 D) 17
Answer» Correct option is (C) 137 \(\because a_1=-3\;\&\;a_2=4\) \(\therefore d=a_2-a_1\) = 4 - (-3) = 4+3 = 7 \(\because a_n=a+(n-1)d\) \(\Rightarrow a_{21}=a_1+(21-1)d\) \((\because n=21)\) \(=-3+20\times7\) \((a_1=-3\;\&\;d=7)\) = -3+140 = 137 Correct option is C) 137

The 21st term of an A.P., whose first two terms are -3 and 4 is ………………A) 143 B) -143C) 137 D) 17

Answer»

Correct option is (C) 137

\(\because a_1=-3\;\&\;a_2=4\)

\(\therefore d=a_2-a_1\)

= 4 - (-3)

= 4+3 = 7

\(\because a_n=a+(n-1)d\)

\(\Rightarrow a_{21}=a_1+(21-1)d\) \((\because n=21)\)

\(=-3+20\times7\) \((a_1=-3\;\&\;d=7)\)

= -3+140 = 137

Correct option is C) 137