Find the 21st term of the Arithmetic Progression (A.P.): -4, -1.5, 1, 3.5,...
FURTHER MATHEMATICS
WAEC 2017
Find the 21st term of the Arithmetic Progression (A.P.): -4, -1.5, 1, 3.5,...
- A. 43.5
- B. 46
- C. 48.5
- D. 51
Correct Answer: B. 46
Explanation
\(T_{n} = a + (n-1)d\)
\( d = T_{2} - T_{1} = T_{3} - T_{2} = -1.5 - (-4) = 2.5\)
\(T_{21} = -4 + (21 - 1) \times 2.5 = -4 + (20\times 2.5) \)
= \(-4 + 50 = 46\)
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