what is the sum of the first 10 terms of the sequence defined by ^an=2n-3?

I assume we have   .....

a_n = 2n -3 

The first term =a₁ =  2(1)-3   = -1

And the 10th term = a₁₀ = 2(10) - 3 = 20 - 3 = 17    

And the sum of the first 10 terms =  10(a₁ + a₁₀)/2  =   10(-1 + 17)/2 = 5(16)  = 80