Question

1+2+3+........+n=45..value of n=?

Answer 1

$\huge{\boxed{\mathtt{\red{ANSWER}}}}$

n(n+1)/2 = 45

n(n+1) = 90

n²+n-90 = 0

n²+10n-9n-90 = 0

n(n+10)-9(n+10) = 0

(n+10)(n-9) = 0

n = 9 (Ans)

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Answer 2

$\huge\underline\purple{\sf Answer}$

To find the value of n ::

$\: \: \: n(n + 1) \div 2 = 45 \\ \\ \: \: \: \: n(n + 1) = 90 \\ \\ \\ \: \: \: \: \: \:n {}^{2} + n - 90 = 0 \\ \\ \: \: \: \: \: n {}^{2} + 10n - 9n - 90 = 0 \\ \\ \: \: \: \:( n + 10) \: (n - 9) = 0 \\ \\ \: \: \: \: \: n = 9$

✴n ==9

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