a₁ = 3 a₂ = 7
a₂ = a₁ + d
d = a₂ - a₁ = 7 - 3 = 4
d = 4
a₁₁ = a₁ + 10d = 3 + 10 * 4 = 3 + 40 = 43
a₁₁ = 43
S=(15/2)(2*(-20)+14*12)=7.5*(-40+168)=960
А=<u>2</u>*<u>2</u>*3*3*3*<u>7</u>=4*27*7=756
d=<u>2*2</u>*2*2*5*<u>7</u>*7*7=16*5*343=27440
НОД =2*2*7=28