Question

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Answer 1

Remark

MusicLover has given you the correct answer and the right method. I am going to present a slightly different way of doing the problem

Step One : find the first term

When n = 1, 2n - 3 = 2(1) - 3 = - 1: a (the first term) is - 1

When n = 2, 2(2) - 3 = 4 - 3 = 1: What this tells you is the d = 2 [1 - -1] = 2

Step Two: Find the last term

L = a + (n - 1)*d

L = -1 + (24- 1) (2)

L = -1 + 23*2 = -1 + 46 = 45 So the last term is 45

Step Three Find the sum

The Summation Formula is (a + L)*n/2

a = -1, L = 45, n = 24

Sum = (-1 + 45)*24/2

Sum = 44 * 12

Sum = 528

Answer 2

First find the total of 2n by using the formula for summation:

( n(n+1))/2

Replace n with 24 and multiply the equation by 2 to get 2n:

2(24(24+1)2) = 2(24*25/2) = 2(600/2) = 600

Now find the total for -3 using the summation for a constant, which is multiplying n by the constant:

-3 x 24 = -72

Now add both summations together:

600 + -72 = 600 - 72 = 528.

The answer is 528.