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EAERCISE i(C)How many terms of the series 42, 36, 30..a ount to 150? |
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Answer» a=42d=36-42=-6S=150Sn=n/2(2a+(n-1)d)150=n/2 (2(42)+(n-1)(-6))300=n(84-6n+6) 300=n(90-6n) 50=n(15-n)n^2-15n+50=0n^2-10n-5n+50=0n(n-10)-5(n-10)=0(n-5)(n-10)=0n=5 n=10 |
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