Đáp án+Giải thích các bước giải:
Câu 1:
$\\a)68.(-37)-63.68\\=68.(-37-63)\\=68.(-100)\\=-6800$
$b)100-99+98-97+....+2-1\\=1+1+1+...+1\\\text{Số số hạng là: [(100-1)+1]:2=50 cặp}\\=>1.50=50$
Câu 2:
$\\a)a) (2x-2^3 ).8^3=8^5\\2x-8=8^5:8^3\\2x-8=64\\2x=64-8\\2x=56\\x=56:2\\x=28$
$\\b) (6x-72):2-84=201\\(6x-72):2=201+84\\(6x-72):2=285\\6x-72=285.2\\6x-72=570\\6x=570+72\\6x=642\\x=642:6\\x=107$
Câu 5:
$\\A=\dfrac{3}{2^2}.\dfrac{8}{3^2}.\dfrac{15}{4^2}...\dfrac{899}{30^2}\\A=\dfrac{1.3}{2^2}.\dfrac{2.4}{3^2}.\dfrac{3.5}{4^2}...\dfrac{29.31}{30^2}\\A=\dfrac{1.3.2.4.3.5...29.31}{2.2.3.3.4.4...30.30}\\A=\dfrac{(2.3.........29.30).(3.4.5......29.31)}{(2.3....29.30).(2.3.4.......29.30)}\\=>A=\dfrac{31}{2.30}=\dfrac{31}{60}$
