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Determine the AP whose third term is 15 and seventh term is 23 |
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Answer» , your answer is A.P = 11 , 13 , 15 , 17 , ... Step-by-step explanation: a3 = 15 a7 = 23 ____________ Let's expand these equations : an = a + (n-1)d a3 = a +(3-1)d = 15 a7 = a + (7-1)d = 23 _______________ a +(2)d = 15______(1) a + (6)d = 23_____(2) ____________ Let's solve these equations (1) & (2) using elimination method. a +2d = 15______(1) - a +6d = 23_____(2) (-4)d = (-8) -4d= -8 d=(-8)/(-4) d=8/4 d=2__(3) Substituting (3) in (1), a+2(2)=15 a+4=15 a=15-4 a=11 We found both a & d . From these we can FIND the A.P : a1 =11 a2 = a+d = 13 a3 = a+2d = 15 a4 = a+3d = 17 & so on... A.P = 11,13,15,17,... Hope it's clear ! |
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