The first and second terms of a linear sequence (A.P) are 3 and 8 respectively.please Determine the least Number of terms of A.P that must be added so that the sum is greater than 250​

Sagot :

Answer:

Least number of terms of A.P will be 10.

Step-by-step explanation:

we know that first term of A.P , a = 3

second term of A.P , b = 8

Now to calculate difference d between first and second term = (8-3) = 5

Let n be the number of terms whose sum is 250 .

Now we know that sum of A.P (Sₙ) is given by

Sₙ = [tex]\frac{n}{2}[/tex] [ 2a + (n-1) d]

substituting values of Sₙ, a and d in above equation we get

250 = [tex]\frac{n}{2}[/tex] [ 2 × 3 + (n-1) 5]

500 = 6n + 5n² -5n

taking equations on one side

5n² + n -500 = 0

now we know that number of terms cannot be a negative number so we will use quadrati formula

n= [tex]\frac{-b }{2a}[/tex] ±[tex]\frac{\sqrt{b^{2}-4ac }}{2a}[/tex]

where a =5 and c = -400 and b =1

n = [tex]\frac{-1+100.4}{10}[/tex]

so n = [tex]\frac{99.4}{10}[/tex]

since n is the number of term so it can only be a whole number so n will be equal to 10.

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