Chứng minh đẳng thức: 1 + 5 + 5^2 + 5^3 + ... +5^2014 + 5^2015 = 5^2016 - 1/4. Tìm x, y biết: 2x + 1/5 = 3y - 2/7 = 2x + 3y - 1/6x

Bai 1:
b) Chung minh dang thuc: 1+5+5^2+5^3+...+5^2014+5^2015=5^2016-1/4
Bai 2:
a) Tim x; y biet: 2x+1/5=3y-2/7=2x+3y-1/6x
Bai 3: Cho tam giac abc deu, diem m thuoc canh bc. Duong thang ke qua m song song voi ac cat ab o p. Duong thang ke qua m song song voi ab cat ac o n.
a) CMR: Tam giac mnf deu
b) Goi o la trong tam tam giac abc. CMR: Goc a bop
c) Goi i la giao diem cua am va pn. CMR: OI la trung truc cua pn
Bai 4: CMR: Trong 8 so tu nhien bat ky co 3 chu so, bao gio cung chon duoc 2 so ma khi viet lien nhau ta duoc so co 6 chu chia het cho 7.
Bai 5: Cho tam giac abc vuong tai a. Tren canh ac lay diem m, tren canh ab lay diem n sao cho gic abm= 1/3 goc abc va goc acn= 1/3 goc acb. Goi o la giao diem cua bm va cn. CMR: Tam giac mon can.