Mathematics: 7.If 18, a, b, - 3 are in A.P., then a+b = ? (1 Point)1212151516161111please give the answer as fast as you can please

lol this is diffuclt.Step-by-step explanation:...

7.If 18, a, b, - 3 are in A.P., then a+b = ? (1

kailiesoto52

30.01.2022

Step-by-step explanation:

General terms in AP

f, f+d, f+2d, f+3d, .... , where f= first term and d= common difference.

The given A.P. : 18, a, b, - 3

here, f= 18

$f+d= a ...(i)\\\\f+2d = b ...(ii)\\\\f+3d= -3 ...(iii)\\\\$

Put f= 18 in (iii) ,

$18+3d=-3\\\\\Rightarrow\ 3d= -3-18\\\\\Rightarrow\ 3d= -21\\\\\Rightarrow\ d=-7$

Put f= 18 and d= -7 in (i) and (ii) , we get

$a=18+(-7)=11\\\\b=18+2(-7)\\\\\Rightarrow\ b=18-14\\\\\Rightarrow\ b=4$

Now, a+b= 11+4=15

Hence, the correct answer is "15".

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