The sum of n terms of an arithmetic sequence with first term 3 and common difference 4 is 1830. Calculate the value of n

Question

anonymous · Answer

My working out: S1830 =n/2 (2x3+(n-1)x4) 
                       1830  = 2n (6+ n x4)
                        n        = 1830/2 x 24

anonymous · Answer

but i got answer completely wrong lol

anonymous · Answer

re-check your second step..

anonymous · Answer

$$Sn = \frac{ n }{ 2 } \times ( 2a + (n-1)d)$$

$$1830 = \frac{ n }{ 2 } \times ( 2*3 + (n-1) 4)$$

anonymous · Answer

n/2(2+4n)
n+2n^2 =1830
2n^2+n-1830=0

(2n+61)(n-30)=0

anonymous · Answer

$$1830*2 = n(6 +4n -4)$$
$$3660 = n (4n +2)$$
$$3660 = 4n ^{2} + 2n$$
$$2n ^{2} + n - 1830 = 0 $$