We know that the formula for the <span>arithmetic sequence is </span><span>an = a1 + (n - 1)*d where a1 is the first term n is the numbers of terms
for n=3 a3=-8 -8=a1+(3-1)*d-----> -8=a1+2*d-----> equation 1
for n=7 a7=32 -32=a1+(7-1)*d----> -32=a1+6*d----> equation 2
multiply equation 2 by -1-----> 32=-a1-6*d------> equation 3
add equation 1 and equation 3 </span>-8=a1+2*d 32=-a1-6*d ---------------- 24=-4*d------> d=-6 -8=a1+2*(-6) (substitute the value of d in equation 1) -8=a1-12-----> a1=-8+12-----> a1=4