gfdes

[tacit ridge]

gfdes

[supple hinge]

@final steeple

here

[final steeple]

Hello

[cursive cargo]

its an hour long video is there anything specific ur confused about

[supple hinge]

i put timestamp

21:43

that qs

@cursive cargo

[final steeple]

This?

[cursive cargo]

u are finding the sum of 3 specific terms in the sequence but not the whole series

[supple hinge]

yea

[cursive cargo]

so think about it

how can you make the sum of those 3 numbers in terms of the arithmetic series formula

[supple hinge]

i undertand the concept

dont know why he doe sthis later

like 8(8-d)(8+d) = 640

@cursive cargo

[final steeple]

Ok umm let's try a diff way

Let the terms be
a-d, a, a+d

Where a is the first term

And d is the common difference

[cursive cargo]

$u(u+d)(u+2d)=-640$

[frosty steppe]

ImOakley

[supple hinge]

can u guys explain further

plsss

[cursive cargo]

$8u(u+2d)=-640$

[final steeple]

a-d + a + a +d is 24

[frosty steppe]

ImOakley

[cursive cargo]

the product of the consecutive terms is -640 right

[supple hinge]

yes

[final steeple]

3a is 24..the middle term is 8

[cursive cargo]

and you know that the first term in question is u

the second is u+d

the third is u+2d

[supple hinge]

u1 * u1+d * u1+2d = -640

'

?

[cursive cargo]

yes

and you know that u+d=8

[supple hinge]

wait a sec

how is u + d 8

[cursive cargo]

because the sum is 24

u+u+d+u+2d=24

simplified its 3u+3d=24

or 3(u+d)=24

or u+d=8

[supple hinge]

u1 + u1 +d + u1 + 2d = 24

3u1 + 3d = 24

u1 + d = 8

[final steeple]

But then u³ + d² = -640

[supple hinge]

ywa got ti

@cursive cargo got it

[final steeple]

After multiplying

[supple hinge]

what next

[final steeple]

... I think

[cursive cargo]

so u use arithmetic series formula

[supple hinge]

un = u1 +(n-1) d

'??

[cursive cargo]

$S_n=\frac{n}{2}(2u_1+(n-1)d)$

is that in the video

[frosty steppe]

ImOakley

[supple hinge]

this is for the sum of all the terms righ

[cursive cargo]

yes

you can let u_1 be the starting term

[supple hinge]

he did not use this if im right

[cursive cargo]

lemme see rq

[supple hinge]

k

[cursive cargo]

oh yeah u dont need the formula

[supple hinge]

i dont understand his concept

[cursive cargo]

we have $8u_1(u_1+2d)=-640$

and $u_1+d=8$

[frosty steppe]

ImOakley

ImOakley

[supple hinge]

u1 + d = 8 i undestood

[cursive cargo]

so just rearrange into $u_1=8-d$

[frosty steppe]

ImOakley

[cursive cargo]

and plug that in

[supple hinge]

ok

what do i plug in

[cursive cargo]

so $8(8-d)(8-d+2d)=-640$

[frosty steppe]

ImOakley

[supple hinge]

i dont understand wht he plugs in

[cursive cargo]

because if $u_1+d=8$ then $u_1=8-d$

[frosty steppe]

ImOakley

[supple hinge]

ye

what does he blug in

[cursive cargo]

so you just replace all the u1 values with 8-d

[supple hinge]

how does -64 come

[cursive cargo]

wdym

this is just simultaneous equations

you know what u1 is in terms of d so you can just replace all the u1 terms with what its equal to

[supple hinge]

can u give me the equation b4 substitition

ill understandf

@cursive cargo

[cursive cargo]

you have $$u_1+d=8$$ and $$u_1(u_1+d)(u_1+2d)=-640$$

[frosty steppe]

ImOakley

[supple hinge]

got this

oh

got it

u1 * 8 * 8 +d = -640

am i correct

$u1 * 8 * 8 +d = -640$

[frosty steppe]

gfdses

[cursive cargo]

yes

you can also put in 8-d for the first u1

so its just d

[supple hinge]

how do u arrive to this step now

@cursive cargo

[cursive cargo]

again u1 is just 8-d

so you can sub that as well

youve gotten yourself to $8u_1(8+d)-640$

[frosty steppe]

ImOakley

[cursive cargo]

so just replace the u1 with 8-d

to get $8(8-d)(8+d)=-640$

[frosty steppe]

ImOakley

[supple hinge]

got it

@cursive cargo tysm bro

[cursive cargo]

np

my friend is also doing ib

[supple hinge]

i think i lack in the basics of math

do u have any recommendations

of what topics to study

[cursive cargo]

wdym i should reccomend topics? are u being taught this?

[supple hinge]

like i jut entered dp rn in ib

i lack basics i feel

what do u recoomend for me to learn

[cursive cargo]

well general algebra is the fundamentals of maths so ig thats important to look at

[supple hinge]

okay will look at that

will hit u up if i have any doubts

do u have any idea how to close thi ticket

[cursive cargo]

Just put the solved tag ig

[slate sapphire]

!done

[tacit ridge]

If you are done with this channel, please mark your problem as solved by typing .close

[supple hinge]

.close