Question

if the common difference of an A.P. is - 6 find a16 - a12

Answer 1

a16=a+15d
a12=a+11d
a16-a12=a+15d-a-11d
=4d
=4×-6
=-24

Answer 2

an=a+(n-1)d
a16-a12
=> {a+(16-1)(-6)}-{a+(12-1)(-6)}
=>{a+(-90}-{a+(-66)}
=>a-90-a+66
=>-90+66
=>-24.