Question

the sum of the first n yerm of an ap whose first term is 8 and common diff. is 20 is equal to the sum of first 2n term of another ap whose first term is -30 anf the common difference is8 find n​

Answer 1

Sn =n/2[2a+(n-1) d]......( Formula)

From Given Condition,

n/2[2×8+(n-1) 20=n[2×-30+(n) 8

n/2[16+20n-20]=n[-60+8n]

n/2[20n-4]=n[-60+8n]

n/2×1/n[20n-4]=-60+8n

1/2[20n-4]=-60+8n

20n-4=2(-60+8n)

20n-4=-120+16n

20n-16n= -120+4n

4n=-126

n= -126/4

n=-63/2