№ 91
а) (–2)2 + (–2)3 + (–2)4 + (–2)5 = 4 – 8 + 16 – 32 = –20;б) 92 – 82 + 72 – 62 = 81 – 64 + 49 – 36 = 30.
вправи поруч
