Answer:
[tex]d=\frac{a_n-a_1}{n-1}[/tex]
Step-by-step explanation:
We need to do some algebraic manipulation to the formula to get our answer [solving for d]:
Note: we will first use distributive property a(b+c) = ab + ac
Now,
[tex]a_n=a_1+d(n-1)\\a_n=a_1+dn-d\\a_n-a_1=dn-d\\a_n-a_1=d(n-1)\\d=\frac{a_n-a_1}{n-1}[/tex]
This is d's expression.