Ok so basically an²+bn-4 was the expression given. We know from the question that when n =1, the first term is -3 and when n=2, the second term is 2
So we hv to do a(1)²+b(1)-4 = -3 which gives us a+b=1
We then had to do the same for when n=2 so it would be a(2)²+b(2)-4 = 2 giving us 4a+2b = 6 which is 2a+b=3 when simplified
Now we have both our simultaneous equations so we just solve for either a or b (im gonna be solving for a for this example)
a+b=1 (multiply by -1) 2a+b=3
-a-b=-1 2a+b=3 a=2
then we just substitute the value of a into the equation for either the first term or second term (im gonna be choosing first)
2(1)²+b(1)-4=-3 2+b-4 = -3 b = -1