2014 · Q21
If aₙ = 3 − 4n, then what is a₁ + a₂ + a₃ + … + aₙ equal to? [1 + 2 + 3 + 4 + … + n = n(n + 1)/2]
Elementary MathematicsAlgebra
- A−n(4n − 3)
- B−n(2n − 1)
- C−n²
- D−n(2n + 1)
Explanation
Sum = 3n − 4·n(n+1)/2 = 3n − 2n(n+1) = n − 2n² = −n(2n − 1).