tim 2 phan so co tu = 1, cac mau duong, biet rang tong cua 2 phan so ay cong voi tich cua chung = 1/2

Tim so tu nhien co 2 chu so biet rang chu so hang chuc lon hon chu so hang don vi la 2 va so do lon hon tong cac binh phuong cac chu so cua no la 1.

a,timx;y sao cho 2^x=4^y-1; 27^y= 3^x+8

b,tim ba phan so biet rang tong cua chung bang 3 3/7(hon so),cac tu cua chung ti le voi 3,4,5,cac mau cua chung ti lt voi5,1,2

chung to rang tong cua 100 so hang dau tien cua day nho hon 1/4

 1/5;1/45;1/117;1/221;1/357;...

tim 1 so tu nhien co 2 chu so biet rang so do lon hon tong cac chu so cua no la 5 don vi

cho s=1 phan 11+1 phan 12+1phan13+.....+1phan19+1phan20

chung minh rang 1phan2 lon hon S lon hon 1

chung minh rang tong cua 1 phan so duong voi so nghich dao cua no ko nho hon 2

Khong thuc hien phep tinh de tim ket qua. Hay chung minh rang cac tong sau lon hon 1

N = \(\frac{21}{90}+\frac{31}{72}+\frac{21}{40}+\frac{-1}{45}+\frac{-1}{50}\)

so cac phan so bang -35/28 ma mau cua chung lon hon 1 va nho hon 19