a2=a1+d=7 => a1=7-dS22= (2a1+21d)/2 * 22 = (2a1+21d)*11=2035(2a1+21d)*11=20352a1+21d= 1852(7-d)+21d=18514-2d+21d=18519d=171d=9a1=7-9=-2