Question

how many first n terms of the sequence 2,10,18 should be added to get 380​

Answer 1

Answer:

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Answer 2

Step-by-step explanation:

GIVEN

• AP → 2,10,18 . . . .
• a = 2
• d = 8
• Sₙ = 380

TO FIND

• n terms to get sum 380 of given AP

SOLUTION

We know that

• Sₙ = n/2 [ 2a + (n - 1) d ]

• n/2 [ 2a + (n - 1) d ] = 380
• n [ 2*2 + (n - 1) 8 ] = 380*2
• n [ 4 + 8n - 8 ] = 760
• 8n² - 4n - 760 = 0
• 2n² - n - 190 = 0
• 2n² - 20n + 19n - 190 = 0
• 2n(n - 10) + 19(n - 10) = 0
• (n - 10) (2n + 19) = 0
• n = 10 or -19/2

Since, nth terms can't be +ve or in fraction so the answer will be 10th term.

Answer 3

Step-by-step explanation:

GIVEN

• AP → 2,10,18 . . . .
• a = 2
• d = 8
• Sₙ = 380

TO FIND

• n terms to get sum 380 of given AP

SOLUTION

We know that

• Sₙ = n/2 [ 2a + (n - 1) d ]

• n/2 [ 2a + (n - 1) d ] = 380
• n [ 2*2 + (n - 1) 8 ] = 380*2
• n [ 4 + 8n - 8 ] = 760
• 8n² - 4n - 760 = 0
• 2n² - n - 190 = 0
• 2n² - 20n + 19n - 190 = 0
• 2n(n - 10) + 19(n - 10) = 0
• (n - 10) (2n + 19) = 0
• n = 10 or -19/2

Since, nth terms can't be +ve or in fraction so the answer will be 10th term.