Plz help

Plz help me in finding 1•2+2•4+3•8+…n•2^n •=multiplication...:-)

#Algebra

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Remember to wrap math in `$` ... `$` or `\[` ... `\]` to ensure proper formatting.
`2 \times 3`	$2 \times 3$
`2^{34}`	$2^{34}$
`a_{i-1}`	$a_{i-1}$
`\frac{2}{3}`	$\frac{2}{3}$
`\sqrt{2}`	$\sqrt{2}$
`\sum_{i=1}^3`	$\sum_{i=1}^3$
`\sin \theta`	$\sin \theta$
`\boxed{123}`	$\boxed{123}$

Comments

What is the sum for $n = 1, 2, 3, 4, 5$ ?

Calvin Lin Staff - 6 years, 3 months ago

Can't get what u want to say.....

Prakher Gaushal - 6 years, 3 months ago

Sir wants to say write the genral term for the series that is and then put corresponding values for n

U Z - 6 years, 3 months ago

slide the series , and multiply it by 2 then take the difference , a g.p will be formed.next is easy

U Z - 6 years, 3 months ago

Sorry ,but I didn't have the patience to write it down in $|LaTeX$ but couldn't let your doubt unattended , sohere's my solution .

P.S. If you find any mistakes, just tell me . I wrote the solution in a hurry !!!

A Former Brilliant Member - 6 years, 3 months ago

Great.

Let me echo my comment in this note

$\sum_{r=1}^{n} rx^r = \frac{x+(nx-n-1)x^{n+1}}{(x-1)^2}$ ) is a useful formula to be aware of, to sum scenarios like this.

Calvin Lin Staff - 6 years, 3 months ago

It think I told the same anyway nice to see your handwriting . Is this your backside of your project file?

U Z - 6 years, 3 months ago

Yeah, correctly guessed :)

A Former Brilliant Member - 6 years, 3 months ago

Thanks

Prakher Gaushal - 5 years, 8 months ago

Math	Appears as
Remember to wrap math in `\(` ... `\)` or `\[` ... `\]` to ensure proper formatting.
`2 \times 3`	$2 \times 3$
`2^{34}`	$2^{34}$
`a_{i-1}`	$a_{i-1}$
`\frac{2}{3}`	$\frac{2}{3}$
`\sqrt{2}`	$\sqrt{2}$
`\sum_{i=1}^3`	$\sum_{i=1}^3$
`\sin \theta`	$\sin \theta$
`\boxed{123}`	$\boxed{123}$