a)(1+2+3+...+20):21 b)(11+11x2+11X2la puterea a2-a...+11x2la puterea a9-a)1023 c)(5la puterea a3-aX10+5la puterea a3x12+...5la puterea a-3-aX100):1001 d)[20+2x(1+2+3+...+19)]:10la puterea a2-a -2la putera a2-a
a) 20*21:2:21=210:21=10 b)dai factor comun pe 11 ⇒ 11(1+2+2^2+....2^9)=11*[2^10-1/2] Nu inteleg * 1023 sau : 1023 d)[20+2*19*20:2]:10^2-2^2=[20(1+19)]:10^2-2^2=20^2:10^2-2^2=2^2-2^2=0
