Question

the sum of 4 term and 8 terms of an AS is 70 and the sum of 6term and 10term is 94.find the sum of first 20 terms.​

Answer 1

Answer:

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Answer:−

GiveN:

Given linear equation x - 5y = 2k

Solution of the equation (5,0)

To FinD:

Value of k.....?

Solution:

It is given that,

Solution of equation = (5,0)

So, putting values of x and y

➝ x - 5y = 2k

➝ 5 - 5 × 0 = 2k

➝ 5 - 0 = 2k

➝ 5 = 2k

Flipping it,

➝ 2k = 5

➝ k = 5/2

So, Value of k = 5/2(A)

Hence, solved !!

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Answer 2

Answer:

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According to the question

a4+a8=70

a6+a10=94

Step-by-step explanation:

Now using the formula of A.P

a+(4-1)d+a+(8-1)d=70

a+3d+a+7d=70

2a+10d=70→→

Divide the eq by 2

a+5d=35→→ (1)

a6+a10=94

a+(6-1)d+a+(10-1)d=94

a+5d+a+9d=94

2a+14d=94

DIVIDING THE EQUATION BY 2

a+7d=47

Equating both the equation

a+5d=35

a+7d=47

we can see that a is cancelling

so by subtracting both the eq

So,

-2d=-12

d=6

now substituting the value of d

in eq (1)

a+5*6=35

a=35-30

a=5

SO THE SUM OF FIRST 20 TERM IS

Sn= n/2[a+(n-1)d]

S20=20/2[5+(20-1)6]

S20=10*[5+19*6]

S20=10*[5+114]

S20=10*119

S20=1190

Hence, the value of first 20 terms is 1190