In an AP if Common difference is $( -4 )$ and seventh term is $4$ then find the first term

Question

I have tried by using the formula

$$a_n=a+(n-1)d$$

And answer is coming -3

I have done it like in this way

$$a_n = a+(n-1)d$$ $$4=a+(4-1)×(-4)$$ $$a=-12/4$$ $$a= -3$$

Answer 1

$$a_7 = a+(7-1)d$$ $$4=a+(7-1)×(-4)$$ $$4 = a-24$$ $$4+24 = a$$

Your mistakes:

• The right $n$ should be $7$.

• Ignoring previous mistake, for some reason, you just go from $4=a-12$ to $a=-12/4$. The right action should have been add $12$ to both sides.