WAEC - Further Mathematics (2021 - No. 25)
The first term of an AP is 4 and the sum of the first three terms is 18. Find the product of the first three terms
292
272
192
172
Giải thích
Using the sum of an AP, S\(_n\) = \(\fra{n}{2}\) [ 2a + (n - 1)d]
S\(_3\) = \(\fra{3}{2}\) [ 2a + (3 - 1)d]
18 = \(\fra{3}{2}\) [ 2a + 2d]
2a + 2d = 12
a = 4
2(4) + 2d = 18 --> 8 + 2d = 12
2d = 4; d = 2
a = 4: a + d
= 4 + 2 = 6
a + 2d = 4 + 2]2]
= 8
product of the terms = 4 * 6 * 8 = 192