How many terms are addeed in 24+20+16+........to take the sum 72
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Answer:
12 should be added with 24+20+16+.....=72
Answered by
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Answer:
Sx = x/2[(2a +(x-1) d]=72
then.. x{2(24)+(x-1)(-4)}=144
48x -4x^2+4x =144
-4x^2 +52x =144
4x^2-52x = -144
4x^2-52x+144 =0
x^2-13x+36 factorising this...
x^2 -4x-9x+36 = 0
x(x-4)+9(x-4)
(x+9),(x-4)
then x = -9,4
-9 is not possible hence 4 is the answer.....
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